# Authorship ethics: an overview of research on the state of practice

Nasir Mehmood Minhas
SERL Sweden, Blekinge Institute of Technology, Karlskrona, Sweden
<EMAIL_ADDRESS>
###### Abstract

Authorship ethics is a central topic of discussion in research ethics fora.
There are various guidelines for authorship (i.e., naming and order). It is
not easy to decide the authorship in the presence of varying authorship
guidelines. This paper gives an overview of research on authorship practices
and issues. It presents a review of 16 empirical research papers published
between 2014 – 2020. The objective is to learn how various research
disciplines handle authorship. What are the authorship practices in various
research disciplines, and what are the issues associated with these practices?

_K_ eywords Research ethics $\cdot$ authorship $\cdot$ practices $\cdot$
issues

##  1 Introduction

The ethics of authorship is well-researched in the health sciences, but it has
got less attention from social scientists [1]. In higher education and
research institutions, authorship credit is considered academic currency [2,
3]. Several organizations, especially the publishers of scientific articles,
provide guidelines on authorship credit. For instance, in health sciences and
its related disciplines, the International Committee of Medical Journal
Editors (ICMJE)111http://www.icmje.org has published the authorship criteria
(see Table 1) as a part of Vancouver protocol. Vancouver protocol includes the
guidelines and recommendations for conducting, reporting, editing, and
publication of scholarly work in medical journals. The influence of ICMJE
criteria is expanding to other disciplines as well [4]. The authorship refers
to two essential aspects that the research team needs to decide about, 1) Who
should be included as an author? (Authorship Naming), 2) Who would be listed
as the first author, and what would be the subsequent positions of co-authors?
(Authorship order). Authorship guidelines suggest that a substantial
contributor would be listed as an author. However, in which order, the
authors’ names should be displayed, guidelines are silent in this regard [5,
6]. Other contributors who do not meet authorship criteria, their names should
have to be listed in the acknowledgment section[4].

The guidelines on who should be an author differ from one organization to
another, and the difference could be within the same research discipline.
These differences could be confusing for the authors and ultimately could lead
to poor authorship decisions [7]. The existing authorship criteria provide a
road-map about authorship naming, but it is hard to find such guidelines
regarding authorship order [8]. Although almost every scientific article
publisher provides authorship criteria, researchers reported disagreements and
unethical practices regarding authorship, for instance, giving authorship to
undeserving persons or ignoring substantial contributors [9]. There is a need
to increase awareness about the ethics of authorship and open up a dialog
among the institutions and researchers [10].

This study aims at investigating the practices and issues related to the
ethics of authorship. A review of empirical articles/papers published between
2014 to 2020 has been conducted. The selection of the primary studies was made
based on the criteria that the presented study should be discussing the
authorship criteria, practices, or issues from the perspective of research
ethics, and it should be a primary study. Hence, the selected primary studies
represent the opinion and experience of researchers regarding the authorship
criteria, practices, and challenges and issues. The selected primary studies
are mainly from health science and its allied disciplines.

The remainder of this paper is organized as follows: Section 2 provides the
summaries of existing reviews on the topic of authorship, Section 4 presents
the findings of this study regarding the authorship criteria/practices, and
Section 5 provides the discussions and conclusions regarding research
questions.

Table 1: ICMJE authorship criteria

ID |  Criterion Description
---|---
C1 |  Substantial contribution to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work
C2 |  Drafting the work or revising it critically for important intellectual content
C3 |  Final approval of the version to be published
C4 |  Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved

  * •

To be an author one should have to fulfill: (C1 & C2 & C3 & C4)

  * •

International Committee of Medical Journal Editors, 2019.

##  2 Related Work

From 2014 to 2021, ten review studies found to be closely related to the topic
of authorship issues and practices [3, 8, 11, 12, 13, 14, 15, 16, 17, 18]. The
selection criteria for the secondary studies was that the selected study
should be a review article/paper on the topics relating to authorship
criteria, authorship practices, or authorship issues. A summary of each
secondary study included in this paper is provided in the following
paragraphs.

Bülow and Helgesson [3] discussed the practices related to gift authorship,
honorary authorship, and hostage authorship. These practices refer to
including a person as an author who does not qualify to be an author. The
authors discussed the probable motives of such practices and termed these
practices as severe ethical concerns. Furthermore, they argue that accepting
the authorship request of an undeserving person in a hostage-like situation
resembles the problem of dirty hands (A term used in political science and
political philosophy). The authors suggest that, if it is unavoidable and
essential to carry out the research, one may accept to include the undeserving
person as an author. Tang [17] criticizes opting for dirty hands even for
bigger benefits for the researchers and the research community. Ranieri [15]
further discusses it from the point of view of junior researchers. Ranieri
agrees with Bülow and Helgesson in their opinion of getting hands dirty in a
hostage-like situation. The author thinks that junior researchers could be
very much in a hostage-like situation related to their supervisors, which
could be an unavoidable situation to them.

Helgesson and Eriksson [8], reviewed the practice of authorship order from the
perspective of research ethics. They concluded that there is no common
understanding of authorship order across disciplines, and authorship
guidelines do not provide any significant criteria regarding authorship order.
The authors argued that the systems based on fixed value assignment for
assessing the authorship position are misleading and unfair. Johal et al.
[11], highlighted the issues of politically motivated co-authorship. They
described that some authors could be listed as co-authors, without any
contribution, because of their influence in research. This would be done
because of some political motives, for instance, career advancement,
increasing the value of article/project by adding senior researchers, etc. The
authors suggested that such practices should be avoided and considered as
corrupt practices.

Kornhaber et al. [12], conducted a review to explore the practices and issues
regarding authorship. They found that honorary (guest/gift) authorship and
ghost authorship are the key authorship issues in health sciences research,
and awarding equal authorship is an increasing trend. Kumar [13] identified
ghost authorship and honorary authorship as concerns to research integrity.
Mandal et al. [14] termed the issues of honorary authorship and ghost
authorship as authorship misconduct. They have provided evidence that a
sizeable number of articles suffer from these problems. The authors also
highlighted the conflicts regarding the authorship order and pointed out that
giving equal credit to the authors is a growing trend. Selbach et al. [16]
presented a review of the research to investigate the issue of authorship and
co-authorship. They have highlighted the unethical authorship practices,
including gift, ghost, and guest authorship. The authors conclude that co-
authorship credit is affected by power relations and personal interests.
Mansourzadeh et al. [18] surveyed Iranian retracted publications indexed in
pubmed. The authors revealed that more than half of the publications are
retracted because of authorship and plagiarism issues.

The existing reviews stressed that practices like gift authorship, guest
authorship, and ghost authorship affect the integrity of collaborative
research. By complementing the presented related work, this study aims to
understand the authorship practices in different disciplines and highlight the
issues concerning research ethics.

##  3 Methodology

###  3.1 Aim and objectives

This review article aims to investigate the authorship issues and practices
from the perspective of research ethics. To fulfill the stated aim, the
following are the objectives:

  1. 1.

To understand the authorship criteria across the disciplines

  2. 2.

To understand the authorship practices in different research disciplines

  3. 3.

To understand the issues related to authorship naming and ordering

###  3.2 Research questions

In the light of defied objectives, the following research questions were
investigated:

  1. RQ1

What have researchers reported about the state of practice regarding
authorship naming and authorship order?

  2. RQ2

What are the issues and unethical authorship practices reported in the
literature?

Table 2: Inclusion Criteria ID |  Criterion
---|---
IC-1 |  The main focus of the selected article should be on research ethics
IC-2 |  The article must be discussing the authorship issues and practice
IC-3 |  The selected article should represent an empirical study (Survey and Case Study)
IC-4 |  The selected article should be published from 2014 to 2020
IC-5 |  The selected article should be in English
Table 3: Exclusion Criteria ID |  Criterion
---|---
EC-1 |  If the main focus of the selected article is not on the research ethics
EC-2 |  If the article is discussing issues other than authorship
EC-3 |  If it is a review article
EC-4 |  If the article was published before 2014
EC-5 |  If the article is written in the languages other than English
EC-6 |  If the full text of the article is not available

###  3.3 Study selection

For the study selection, I applied the search string (( "research ethics" )
AND ( "authorship ethics" OR "authorship perception" OR "authorship issues" OR
"authorship practices" OR "co-authorship" OR "authorship credit" OR
"authorship criteria" ))) in Scopus222www.scopus.com for the year 2014 and
2020. Database searches returned a total of 180 articles, and after the title
screening, 43 articles were retrieved. After reading the abstract and applying
the inclusion criteria (See Tables 2 and 3), 16 primary studies were selected
for further review and analysis.

Table 4: Data extraction form No. |  Item |  Data extracted
---|---|---
1 |  General information |  Study title, abstract, publication year, venue, country
2 |  Author affiliations |  Departments and/or faculties of the study authors
3 |  Study participants |  Early career, mid career, or senior researchers
4 |  Field |  Field of research where study has been conducted (e.g., Medical, social science, etc.)
5 |  Study type |  Case study, experiment or survey, or other
6 |  Focus |  Primary focus of the investigation
7 |  Findings |  Key findings of the study
8 |  Challenges and issues |  Specific challenges and/or issues regarding authorship ethics highlighted in the findings of the study (e.g., authorship naming and ordering, definition of authorship, etc.)

###  3.4 Data extraction

Table 4 presents the data extraction form. The information extracted from the
primary studies was stored in the excel sheets. The extracted information
includes metadata of included primary studies, authors data, subjects of the
study. The focus was to extract the data related to the study’s primary focus,
key findings, and challenges and issues concerning the ethics of authorship.

###  3.5 Study limitations

The representativeness of the findings could be a limitation of this study as
the searches performed in only a single database (Scopus) and are time-
bounded. Therefore the author does not claim exhaustive searches of the
primary studies. However, the consistency of findings somehow minimizes the
study’s limitation. Another limitation of this study could be the quality of
results and the researcher’s bias. This limitation is minimized by involving
two senior researchers who reviewed the results and provided their feedback.

Table 5: Included primary studies

Study ID |  Title |  Focus |  Method |  Field11footnotemark: 1 |  Year
---|---|---|---|---|---
Decullier and Maisonneuve [19] |  Have ignorance and abuse of authorship criteria decreased over the past 15 years? |  To study the awareness of clinical researchers about the authorship ethics and ICMJE criteria. |  Survey |  Medical |  2020
Smith et al. [5] |  Misconduct and Misbehavior Related to Authorship Disagreements in Collaborative Science |  Disagreements regarding authorship naming and ordering. Factors that cause disagreements, and misconduct and misbehavior associated with these disagreements. |  Survey |  Science & Engineering |  2019
Rees et al. [20] |  Importance of authorship and inappropriate authorship assignment in paediatric research in low- and middle-income countries |  To understand the similarities and differences among the researchers of pediatrics science from low- and middle-income countries and high income countries regarding the importance of authorship position, and inappropriate authorship assignments. |  Survey |  Medical |  2019
Breet et al. [21] |  Academic and Scientific Authorship Practices: A Survey Among South African Researchers |  To investigate the understanding of the researchers regarding authorship criteria and gauge their ability to apply it in the multi-authored studies. |  Survey |  Science & Engineering |  2018
Helgesson et al. [22] |  Misuse of Co-authorship in Medical Theses in Sweden |  To explore the issues of authorship that have encountered by the researchers who have recently completed their doctoral thesis. |  Survey |  Medical |  2018
Alshogran and Al-Delaimy [23] |  Understanding of International Committee of Medical Journal Editors Authorship Criteria Among Faculty Members of Pharmacy and Other Health Sciences in Jordan |  To evaluate the perceptions, attitudes, and practices of researchers concerning authorship criteria. |  Survey |  Medical |  2018
Uijtdehaage et al. [24] |  Whose paper is it anyway? Authorship criteria according to established scholars in health professions education |  To represent the opinion of leading researchers regarding an appropriate criteria of authorship. |  Survey |  Medical |  2018
Mavis et al. [6] |  Authorship Order in Medical Education Publications: In Search of Practical Guidance for the Community |  To study the practices regarding authorship order and to learn the way researchers from US medical education decide the authorship order. |  Survey |  Medical |  2018
Macfarlane [1] |  The ethics of multiple authorship: power, performativity and the gift economy |  To study the attitude of researchers representing higher education faculties regarding multiple authorship. |  Case-based Survey |  Education (Social Sciences) |  2017
Elliott et al. [25] |  Honorary Authorship Practices in Environmental Science Teams: Structural and Cultural Factors and Solutions |  To represent the opinion of researchers regarding authorship policies and practices. |  Interview-based Survey |  Environmental Sciences |  2017
Kumar and Ratnavelu [26] |  Perceptions of scholars in the field of economics on co-authorship associations: Evidence from an international survey |  To know the perceptions of economics researchers regarding co-authorship, authorship ordering and authorship practices. |  Survey |  Economics (Social Sciences) |  2016
Bozeman and Youtie [27] |  Trouble in Paradise: Problems in Academic Research Co-authoring |  To investigate the exclusion of the deserving individuals from co-authorship and unfair inclusion of co-authors. |  Interview based study |  Science & Engineering |  2016
Das et al. [28] |  Knowledge on ethical authorship: A comparative study between medical and pharmacy faculty |  To access the understanding of Indian health sciences researchers regarding the ethics of authorship. |  Survey |  Medical |  2016
Šupak-Smolčić et al. [29] |  ICMJE authorship criteria are not met in a substantial proportion of manuscripts submitted to Biochemia Medica |  To assess the level of implementation of ICMJE criteria and to investigate the authorship violations among the researchers from medical sciences. |  Survey |  Medical |  2015
Seeman and House [30] |  Authorship Issues and Conflict in the U.S. Academic Chemical Community |  To investigate the authorship conflicts between early career researchers and their seniors. |  Survey |  Chemistry |  2015
Al-Herz et al. [31] |  Honorary authorship in biomedical journals: How common is it and why does it exist? |  To determine the presence of honorary authorship in biomedical publications and identify the factors that lead to its existence. |  Survey |  Medical |  2014

  * 1

Medical represents all the disciplines that are related to medicine and health
sciences.

##  4 Results

Table 5 presents a summary of the primary studies reviewed in this report, and
Table 6 presents the definitions of key terms found in the selected primary
studies. A majority of the primary studies (9 of 16) are representing the
medical (all disciplines related to health sciences), followed by science and
engineering (3 of 16), then social sciences (2 of 16), and finally, one study
each from chemistry and environmental sciences. The findings of this review
are presented in subsections 4.1 and 4.2.

Table 6: Definition of terms concerning authorship practices Issue |  Definition | Ref
---|---|---
Authorship |  Authorship refers to identifying individuals who have a substantial contribution to the conducting and reporting of research and stand responsible for the work while receiving due credit. | [6, 5, 29]
Ghost authorship |  Denying authorship to one who has significant contributions in the study or who fulfill the authorship criteria. | [24, 22, 27, 30, 1, 23]
Gift authorship |  Granting authorship as favor to one who does not qualifies the authorship criteria. | [24, 5, 1, 22, 28, 23]
Guest/Honorary authorship |  Granting authorship to senior individuals as courtesy or to add prestige to the paper. | [24, 22, 25, 26, 27, 31, 23, 19]
Hostage authorship |  Including an undeserving individual as author because of unavoidable pressure. | [1, 28, 23, 24]

###  4.1 Authorship criteria

A person would be listed as an author in a scientific paper if she has a
significant contribution, and it is essential to measure the contribution
based on some defined criteria. Authorship criteria provide the basis to
assess the contribution of an individual working in a research team. Various
publishers of scientific journals provide guidelines regarding authorship
criteria. Variations exist in the authorship criteria across disciplines and
publishers. Such differences are even visible for publishers within the same
subject [24, 5]. A majority of the authors of our selected studies referred to
the authorship criteria published by ICMJE (see Table 1) [5, 20, 21, 22, 23,
24, 1, 28, 29]. The ICMJE criteria are accepted worldwide by the journals from
medicine and related health sciences disciplines. The authors from the
disciplines other than medicine and health sciences are also referring to the
ICMJE criteria [5, 21, 1].

Authorship naming and order are the two primary aspects, and the research team
needs to decide carefully about authorship naming and order. Poor or careless
decision-making can lead to disagreements and unethical practices. The
following subsections discuss the state of practice regarding authorship
naming and order.

####  4.1.1 Authorship naming criteria: State of practice

Many authors reported that authorship criteria are not followed in their
complete letter and spirit while naming an author. Some of the instances are
reported in the following paragraphs.

Helgesson et al. [22] surveyed with the researchers who have recently
completed their doctoral degrees in medicine. The authors investigated the
authorship issues concerning compliance to the authorship guidelines.
According to the majority (53%) of the respondents, ICMJE authorship
guidelines were not respected in at least one of their articles. However, a
vast majority (80%) of the respondents reported their awareness of authorship
guidelines. Breet et al. [21] conducted a survey with the science and
engineering researchers of South Africa and found that 80% of the survey
respondents are aware of authorship guidelines 52% confirmed that they found
it easy to implement the authorship criteria. Alshogran et al. [23]
investigated the understanding of ICMJE authorship criteria among the health
sciences researchers of Jordan. The authors revealed that only 27% of the
respondents reported their awareness about the ICMJE guidelines. However, most
of the respondents (77%) agreed that authorship should be granted only if one
qualifies the ICMJE authorship criteria. In a study with the research leaders
from the health profession, Uijtdehaage et al. [24] reported that 58% of the
respondents correctly identified the ICMJE authorship criteria. There were
some assumptions of the senior researchers regarding authorship. For instance,
14% of senior researchers considered supervising or leading a research team
qualifies one to be an author. Similarly, 14% of them believed that drafting a
manuscript should not be regarded as a criterion of authorship. According to
Uijtdehaage et al., these assumptions are not aligned with the defined
standards. Macfarlane [1] conducted a case-based survey to understand the
viewpoint of academics from social sciences regarding ICMJE authorship
criteria. The results revealed that 77% of the participants agreed with the
first criterion of ICMJE, 48% were in favor of the second criterion, 77%
supported the third criterion, and only 13% thought that the fourth criterion
is sufficient to be an author. The ultimate perception of the participants
was, anyone who has a substantial contribution is a legitimate author, but the
most difficult part is to define the substantial contribution. In an
interview-based study with six research teams from environmental sciences,
Elliott et al. [25] revealed that half of the participants are using formal
written policies and the other half are using informal procedures to decide
who among the team members should be named as an author. The authors reported
that these procedures (formal or informal) are overinclusive. The primary
cause of being overinclusive is the difficulties in determining the extent of
the contribution. In a survey with the medical and pharmacy faculties of India
[28], it is reported that only 22% of medical and 39% of pharmacy faculty
members were aware of COPE (Committee On Publication Ethics) or ICMJE
guidelines on authorship. In a survey of articles submitted with a medical
journal (2013 to 2015), Šupak-Smolčić et al. [29] analyzed the self-reported
contribution statements to assess the conformance with ICMJE criteria. They
reported that 61% of the researchers were utterly following the ICMJE
criteria, while 9% of them were not following it at all. Furthermore, it is
revealed that in the self-reported contribution statements where the authors
claimed to fulfill the authorship criteria, only 49% of them were qualified
according to ICMJE criteria.

From the discussion on the findings of existing primary studies, it could be
concluded that the authorship criteria are not followed in the majority of the
cases, and there is a lack of awareness regarding the authorship criteria.

####  4.1.2 Authorship order: State of practice

Authorship order is translated differently in different academic / research
disciplines. For instance, in some research areas, the authors’ names are
listed in alphabetical order. In many research domains, the authorship order
exhibits the authors’ contribution to the study. Various research and academic
institutions use the authorship order to determine the scientific merit of the
individuals [5].

In a survey-based study, Rees et al. [20] revealed that there is a contrast
between the authors from low-and-middle-income countries (LMIC) and high-
income countries (HIC) regarding authorship order. Authors representing LMIC
perceive the first position as the most important, whereas HIC representatives
consider the last position as most significant. In a survey with the Jordanian
health sciences, researchers Alshogran et al. [23] revealed that 79% of
respondents agreed that the authorship order should be based on the respective
contributions, and the decision should be taken jointly by all authors. In a
survey with the researchers, Mavis et al. [6] found that a majority of the
respondents (86%) supported that the authors should be listed in the
decreasing of contribution, starting with the most substantial contributor as
the first author. 95% of the respondents emphasized an agreement between the
contributors regarding the authorship order. Furthermore, 94% of the
respondents were against the alphabetical listing of authors, and 74% believed
that first, second, and corresponding authors are the significant
contributors. In a case-based survey by Macfarlane [1], 32% of the survey
respondents suggest to award the first authorship to a person who needs it for
career advancement (e.g., research student), 17% suggested to use alphabetical
order, and 6% respondents voted to award the first authorship to the senior
team member. Macfarlane coined the terms of gift ordering and power order. The
first refers to decide the authors’ order by career considerations instead of
intellectual contributions. In contrast, the second term refers to determining
the authors’ order based on the hierarchy within the research team. In a
multi-nation survey with the economics researchers, Kumar and Ratnavelu [26]
revealed that although it is believed that economics researchers follow the
alphabetical order of authorship, however, to decide the authorship order, 35%
of the survey respondents measure the authors’ contribution.

The above discussion concludes that authorship order has significant
importance in a majority of research/academic disciplines. The first, second,
and corresponding authors are considered to be leading contributors in an
article. In most cases, the authorship order is decided based on the
respective contribution of the authors. In some disciplines (e.g., economics),
authors’ names are listed in alphabetical order.

###  4.2 Authorship issues

####  4.2.1 Authorship disagreements

In an online survey, Smith et al. [5] investigated authorship naming and
ordering disagreements. 46% of the respondents reported the disagreements
regarding authorship naming, whereas 38% of them described the disagreements
concerning authorship order. Furthermore, it is revealed that the likelihood
of disagreements varies across the disciplines, career levels, and gender. For
instance, mid-career researchers are more involved in disagreements than
senior researchers, and early career researchers are rarely involved in such
issues. On the gender side, compared to male researchers, most of the events
of disagreements were reported by the female researchers. Results show that
for authorship naming, the most critical factor that causes disagreements is
valuing an individual’s contribution. The cause of these disagreements could
be differing ethics, lack of discussions and agreement within the team, and
lack of clarity about criteria. Breet et al. [21] highlighted the researchers’
experience regarding the authorship disagreements, 59% of their survey
respondents confirmed that they had encountered disagreements regarding
authorship naming, and 48% of the respondents reported such disagreements in
authorship order. The survey revealed that most disagreements were due to
different ways of measuring the contributions. Furthermore, female researchers
were highlighting more disagreements concerning authorship order compared to
authorship naming. Alshogran et al. [23] reported that a majority of the
respondents of their survey-based study reported disagreements on authorship.
Based on the experiences of the researchers, Bozeman and Jan [27] discussed
the events of disagreements in the authorship order. In the reported
incidents, the junior or middle career researchers were the complainants
against the senior researchers. Seeman and House [30] reported authorship
conflicts among the junior researchers and their seniors, colleagues from the
same institution, and colleagues from different institutions. A small number
of affectees took their concerns to the offending individuals, while most did
not take this initiative because of fear of not getting a positive outcome and
being in an undermined situation.

From the findings of the reviewed studies, it could be concluded that the
majority of disagreements relate to authorship naming. However, such conflicts
also exist regarding the authorship order. The complaining individuals are
primarily early- and mid-career researchers and they have such complaints
against the senior members of their research teams. Furthermore, the majority
of these disagreements were reported by female researchers.

####  4.2.2 Unethical authorship practices

In a survey study [20], it is revealed that a majority of the researchers have
an opinion that, in most cases, authorship order is assigned inappropriately,
and a sizeable number of researchers told that they did accept the wrong
author-order to avoid the conflicts with the collaborators. Helgesson et al.
[22] revealed that 28% of the survey respondents experienced the handling of
authorship order without merit. Furthermore, the respondents reported the
inclusion of one or more authors without having a substantial contribution.
Alshogran et al. [23] revealed that in their survey-based study, 30% of the
respondents claimed that they were forced to add an undeserving author. It is
also reported that the incorrect placing of authors and issues of the ghost,
gift, or guest authors are common in health sciences researchers of Jordan.
Uijtdehaage et al. [24] reported that 63% of their survey respondents told
that without contributing, senior-level administrators are listed as co-
authors in the papers of faculty working under them. 60% of respondents said
that they witness awarding gift authorship to the individual who did not have
any input in the research work. Honorary authorship was also reported by the
majority (69%) of the survey respondents, whereas, 4% of the respondents
consider the award of honorary authorship as ethical. A large number of
respondents (51%) reported facing pressures regarding the authorship order.
Furthermore, the authors also discussed the problem of ghost authorship, not
giving authorship to the contributors who fulfill the authorship criteria.
Macfarlane [1] reported the experiences of respondents regarding unethical
practices in a case-based survey. The reported events were, denying authorship
to a substantial contributor or given minor credit (ghost authorship),
awarding authorship to supervisors who did not contribute to the work (gift
authorship), and pressures from seniors/heads to include them as authors with
no contribution (hostage authorship). In an interview-based study with the
senior and early career researchers, Elliott et al. [25] reported the
inappropriate authorship practices within the research teams. For instance,
awarding authorship to all team members, regardless of having significant,
marginal, or no contributions in the article, the authors termed the
phenomenon as honorary authorship. In a multi-nation survey with the economics
researchers, Kumar and Ratnavelu [26] also pointed out the practice of
awarding honorary authorship. In an interview-based study with science and
engineering researchers, Bozeman and Jan [27] shared the stories of different
researchers regarding the issues of excluding the deserving individuals from
the authors’ list (ghost authorship) and awarding authorship to non-deserving
individuals (guest authorship). In a comparative survey between medical and
pharmacy faculty members in India, Das et al. [28] revealed that 89% of
medical and 37% of pharmacy faculty members were involved in awarding gift
authorship to their professors and head of departments. Similarly, 81% of
medical and 29% of pharmacy faculty members were pressurized by the seniors to
include their names in the articles (Hostage authorship). In a survey with the
chemistry researchers from the US, Seeman and House [30] reported ghost
authorship practice. The authors found that 50% of the respondents were not
included as a co-author, although they had contributed significantly to work.
35% reported that their supervisor did not acknowledge their contribution. 41%
were complaining about a colleague from their institution, while 42% said that
a colleague from another institution did this. In a survey with the medical
researchers, Al-Herz et al. [31] investigated honorary authors and reasons to
award the honorary authorship. The results revealed that 33% of respondents
awarded honorary authorship to others. The reasons for the award of honorary
authorship in terms of percentage of respondents were, complimentary award by
39%, avoiding conflicts at workplace 16%, and to increase the chance of
article acceptance 7%

The above discussion leads to the fact that unethical authorship practices are
common in almost all research fields. Regardless of gender or experience, the
researchers are reportedly involved in such activities. In some cases, the
researchers were in favor of some of the practices. For instance, awarding
authorship to an undeserving individual in a hostage like situation, or
gifting authorship to an individual for the career benefits.

##  5 Discussion and Conclusion

This paper reviewed the empirical studies on the topic of authorship published
from 2014 to 2019. Given that searches are limited and may not always find all
relevant studies, it is a limitation of this study. This limitation did not
affect the findings since the results obtained from the papers are consistent
and reveal a pattern. The selected studies investigated the state of practice
regarding the ethics of authorship. The following paragraphs summarize the
findings.

Regarding RQ1 (“What have researchers reported about the state of practice
regarding authorship naming and authorship order?"), the intention was to
learn about the understanding of researchers regarding authorship criteria and
to investigate the current practices associated with authorship naming and
authorship order. From the studies of different disciplines, it is revealed
that the most followed authorship criteria is the one defined by ICMJE, and
along with the medical sciences, researchers from other subjects are also
referring to it. However, studies revealed that a majority of researchers are
not following the authorship criteria in their papers. One of the reasons in
this regard is the awareness of the researchers, especially from low- and
middle-income countries. Authorship criteria provide the guide to decide who
should be named as an author in a scientific study. However, the criteria do
not provide any support regarding the authorship order. The practices related
to authorship order vary among the different disciplines. For instance, in
some research disciplines, authors’ names are listed in alphabetical order,
whereas others use the assessed value of the contribution to decide the
author’s order. In most cases, first, second, and corresponding author
positions are considered significant. In practice, two extremes were revealed,
1) strictly following the authorship criteria, and 2) being overinclusive. In
the first case, by strictly applying the ICMJE authorship criteria, there is
high likelihood that some members may not be included as authors of a
scientific study because of failing to meet some points of criteria. Hence,
maybe denying authorship to a deserving individual. Whereas in the second
case, it is revealed that every member of the research team will be included
as an author at the first stage. Later, members can decide to be on the
authors’ list or request to pull their names from the list. Ultimately, maybe
awarding authorship to an undeserving person. These two scenarios are the
basis of the majority of the unethical authorship practices.

Concerning RQ2 (“What are the issues and unethical authorship practices
reported in the literature?"), the focus was to investigate the issues
regarding authorship that researchers are facing in multi-authored studies.
This report highlights two aspects, 1) authorship disagreements and 2)
unethical authorship practices. The research reports various disagreements
concerning authorship, mainly the conflicts relate to authorship naming and
authorship order. In most cases, the conflicts were reported by early career
and mid-career researchers, and they were complaining about the events of
disagreements with their seniors. However, there are only a few instances
where the mid-career researchers took up the conflicting issues, while most
early-career researchers avoided doing so. The stated reasons for not bringing
up the disagreements were fear of affecting the working relationships with the
colleagues, expectations of positive outcomes, and being in a hostile
situation. It has revealed that various unethical practices are associated
with authorship, for instance, awarding authorship to an undeserving
individual (gift authorship, guest or honorary authorship), awarding
authorship under pressure (hostage authorship), and denying authorship to a
substantial contributor (ghost authorship).

###  5.1 Authorship practice in software engineering

As a software engineering researcher, the author was interested in reviewing
the studies presenting the state of authorship practice in software
engineering or computer science disciplines. The author could not find even a
single study investigating the authorship practice in these disciplines.
Therefore, the author could not reflect on the state of authorship practice in
software engineering and computer science. However, considering the reports
from other disciplines, it is assumed that there may be ethical issues
associated with authorship practice in these research areas. Empirical
investigations from these research disciplines are needed to present the state
of practice on the ethics of authorship, and such studies could help create an
awareness among the research community.

###  5.2 Concluding note

From the findings of existing empirical studies on authorship, it is concluded
that there is a need to create awareness among the researchers regarding
authorship ethics and criteria. In this regard, universities, research
institutions, and senior researchers have to take the lead. The authorship
guidelines need to be published at the institutional level, and every early
career researcher (e.g., Ph.D. student) should have to be provided with
training on research ethics. The institutions, departments, and research
groups need to define clear policy guidelines regarding authorship (naming and
ordering). Considering the guidelines, at the beginning of every research
venture, the research team members have to make sure to define the team’s
policy on authorship. And to identify the substantial contributor(s), the
contribution analysis should have to be done after every phase of research
work. In this regard, web-based task assignment and tracking applications can
help assign and monitor the tasks to the team members. At the departmental
level, there could be an oversight committee that could help in the resolution
of authorship conflicts. The editors of scientific journals may encourage the
submission of a contribution statement duly signed by all contributors.

###  5.3 Future work

The author is currently working on a survey-based study that would be
conducted with software engineering researchers. The aim is to investigate
authorship practices and issues.

## Data Availability

It is a review paper, and all included primary studies are listed in Table 5
and are available online. Furthermore, data extracted from the included papers
are comprehensively presented in Section 4 and discussed in Section 5.

## Acknowledgement

The author would like to thank Prof. Jürgen Börstler and Prof. Claes Wohlin,
for their valuable feedback on initial phases of the review and subsequently
on the drafts of this paper.

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Research, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany

# A strain-controlled magnetostrictive pseudo spin valve

Vadym Iurchuk<EMAIL_ADDRESS>Institut de Physique et Chimie des Matériaux
de Strasbourg (IPCMS), UMR 7504 CNRS, Université de Strasbourg, 23 rue du
Loess, 67034, Strasbourg, France  Julien Bran  Institut de Physique et Chimie
des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS, Université de Strasbourg,
23 rue du Loess, 67034, Strasbourg, France  Manuel Acosta  Institut de
Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS,
Université de Strasbourg, 23 rue du Loess, 67034, Strasbourg, France  Bohdan
Kundys  Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS),
UMR 7504 CNRS, Université de Strasbourg, 23 rue du Loess, 67034, Strasbourg,
France

###### Abstract

Electric-field control of magnetism via inverse magnetostrictive effect is an
efficient path towards improving energy-efficient storage and sensing devices
based on giant magnetoresistance effect. In this letter, we report on lateral
electric-field driven strain-mediated modulation of magnetic properties in
Co/Cu/Py pseudo spin valve grown on ferroelectric
0.7Pb[Mg1/3Nb2/3)]O3–0.3PbTiO3 substrate. We show a decrease of the giant
magnetoresistance ratio of the pseudo spin valve with increasing electric
field, which is attributed to the deviation of the Co layer magnetization from
the initial direction due to strain-induced magnetoelastic anisotropy
contribution. Additionally, we demonstrate that strain-induced magnetic
anisotropy effectively shifts the switching field of the magnetostrictive Co
layer, while keeping the switching field of the nearly zero-magnetostrictive
Py layer unaffected due to its negligible magnetostriction constant. We argue
that magnetostrictively optimized magnetic films in properly engineered
multilayered structures can offer a path to enhancing the selective magnetic
switching in spintronic devices.

Modern spintronics demands for high-stability, low-power, fast-switching
devices operable at room temperature. Advanced approaches of magnetization
control tend to promote alternative to magnetic field methods to get access to
magnetic state of spintronic elements, e.g. magnetic field sensors or
magnetoresistive memory cells Bibes and Barthélémy (2008); Shen  _et al._
(2016); Vaz (2012); Binek and Doudin (2005). One of the promising ways is
electric-field control of magnetic properties in artificial
ferroelectric/ferromagnetic heterostructures via strain-mediated
magnetoelectric effects Domann  _et al._ (2018). Strain-controlled tuning of
magnetism has become a hot topic of recent theoretical Roy  _et al._ (2011a,
b, 2012); Roy (2013); Jia  _et al._ (2012); Biswas  _et al._ (2014); Wang  _et
al._ (2017, 2018); Schneider  _et al._ (2019) and experimental Bihler  _et
al._ (2008); Ranieri  _et al._ (2008); Rushforth  _et al._ (2008); Brandlmaier
_et al._ (2008, 2011, 2012); Liu  _et al._ (2011); Zhang (2012); Sando  _et
al._ (2013); Lahtinen  _et al._ (2012); Liu  _et al._ (2013); Lei  _et al._
(2013); Buzzi  _et al._ (2013); Zhu  _et al._ (2013); Peng  _et al._ (2018);
Zhu  _et al._ (2021); Iurchuk  _et al._ (2014, 2015) studies, where a
piezoelectric strain is shown to modify magnetic anisotropy, coercivity,
anisotropic magnetoresistance (AMR) or switch the magnetization direction of
the magnetic component of magnetoelectric heterostructures. From the practical
point of view, it is important to utilize this effect in spintronic
structures, e.g. in giant magnetoresistive (GMR) multilayers or magnetic
tunnel junctions. Several successful attempts were done to confirm the
viability of the strain-mediated manipulation of giant or tunneling
magnetoresistance in magnetic multilayers grown on ferroelectric Li  _et al._
(2014); Roy (2015); Chen  _et al._ (2019); Liu  _et al._ (2021) or
mechanically flexible Liu  _et al._ (2016); Hashimoto  _et al._ (2018)
substrates. However, commonly used design of the magnetic devices with
magnetostrictive functionality requires the presence of the pinning
antiferromagnetic layer in the magnetic stack to ensure a separate access and
control over the magnetic layers.

In this letter, we report on lateral electric-field induced changes of GMR
properties in PMN-PT/Co/Cu/Py (Py=Ni80Fe20) heterostructure comprising
magnetic layers with different magnetostriction constants. We show that the
GMR ratio of the Co/Cu/Py pseudo spin valve (PSV) as well as the switching
field of the Co layer decrease as electric-field induced piezoelectric strain
increases. We attribute this effect to the strain-induced modification of the
magnetic anisotropy of the Co layer through the inverse magnetostrictive
(magnetoelastic) effect. On the other hand, the switching field of the Py
layer changes only scarcely under strain, which is a consequence of known
close-to-zero magnetostriction of the Ni80Fe20 Permalloy compound. This result
paves a way to strain-controlled manipulation of magnetic and magnetotransport
properties of PSV tri-layers with properly adjusted magnetostrictive
properties of the constituent magnetic layers.

The composition of the PSV tri-layer was chosen as Co/Cu/Py, motivated by
relatively large magnetostriction constant of Co –20 to –60 ppm Klokholm and
Aboaf (1982) depending on the crystallographic phase admixture in the
sputtered polycrystalline films) and negligible magnetostriction constant of
nearly zero-magnetostrictive Py (notably its Ni80Fe20 compound with
$\lambda_{s}\approx$ 1.5 ppm) Reekstin (1967); Klokholm and Aboaf (1981). The
Co/Cu/Py PSV was deposited onto 500 µm thick polished ferroelectric
0.7Pb[Mg1/3Nb2/3)]O3–0.3PbTiO3 (PMN–PT) single crystalline substrate by
magnetron sputtering at a base pressure of $3\times 10^{-7}$ mbar. A shadow
mask was used to obtain patterned $\sim$950 $\times$ 35 $\mu$m2 rectangular
stripes. No magnetic field was applied during the deposition. Ti(5 nm)/Au(50
nm) surface electrodes were deposited aside the stripe (see Fig. 1(a)) to
generate piezoelectric strain as a result of the lateral electric field
stimulus of the ferroelectric substrate. Two-probe magnetoresistance (MR)
measurements were carried out in current-in-plane geometry with magnetic field
applied parallel to the long axis of the PSV stripe. Fig. 1(a) shows the
schematics of the sample under study and the geometry of the experiment.

Figure 1: (a) Schematics of the Co/Cu/Py pseudo spin valve stripe fabricated
on PMN–PT single crystalline substrate. (b) Magnetic and magnetoresistance
hysteresis loops measured on Si/SiO2/Co(5)/Cu(4.5)/Py(5) (thicknesses is nm)
(same deposition batch with PMN-PT/Co/Cu/Py) showing distinct and well-
separated switching fields of Py (green arrow) and Co (red arrow) layers. (c)
Ferroelectric polarization and corresponding displacement current of PMN-PT
single crystal measured in the lateral geometry as shown in (a). (d, e)
Schematic representation of the distorted PMN–PT rhombohedral crystal
structure with highlighted (blue arrows) polarization directions in out-of-
plane (d) and in-plane (e) ferroelectric domains. Red arrows denote net
polarization directions. Lattice distortions are exaggerated.

A set of polycrystalline tri-layers was prepared varying the thicknesses of
the magnetic and the spacing layers. The optimal composition for the presented
study was chosen to be Co(5)/Cu(4.5)/Py(5) (thicknesses are in nm) since it
provides both significant GMR ratio and clear separation between the coercive
fields of Co and Py layers. Fig. 1(b, top graph) shows the room-temperature
magnetic hysteresis of the PSV tri-layer performed on the reference sample
(grown on Si/SiO2 substrate in the same deposition batch with PMN-PT). We
observe clear and relatively sharp switching of both layers forming a well-
defined plateau between the two coercive fields corresponding to the
magnetization reversal of Py (red arrow) and Co (green arrow) layers
respectively. The MR loop measured on the extended Co/Cu/Py tri-layer on
Si/SiO2 perfectly correlates with the magnetic hysteresis (see Fig. 1(b,
bottom graph)), yielding a GMR ratio of 2.3$\%$ at room temperature.

An unpoled rhombohedral (011)PMN–PT ferroelectric single crystal (commercially
available from Crystal GmbH) was used as a functional substrate to generate an
electric-field-induced strain, which is transferred to the PSV tri-layer grown
atop. The PMN–PT composition is in the vicinity of the ferroelectric
morphotropic phase boundary Guo  _et al._ (2002) where large piezoelectric
coefficients Zhang  _et al._ (2008) are expected allowing for large strains
when moderate electric fields are applied to the crystal. Fig. 1(c) shows the
ferroelectric polarization and the electrical displacement current loops vs.
applied electric field measured in the lateral geometry (see Fig. 1(a)).
Ferroelectric coercive field for this particular geometry is $E_{C}$ = 0.43
MV/m which is approximately twice higher comparing to the typical values for
the out-of-plane geometry, when the electric field is applied across the bulk
of the substrate Zhang  _et al._ (2008); Wu  _et al._ (2011). The origin of
this discrepancy is likely attributed to the sub-surface ferroelectric domains
growth and reversal, where a net polarization switches only in topmost thin
PMN–PT layer while the bulk ferroelectric state remains unchanged.

Ferroelectric polarization reversal is accompanied by ferroelastic domains
switching which leads to the distortions of the crystal lattice. Schematic
images of polarization orientations in PMN–PT crystal with rhombohedral
structure are presented in Fig. 1(d,e). When no electric field is applied the
spontaneous ferroelectric polarization is aligned along one of the eight
equivalent $<$111$>$ directions (blue arrows), creating ferroelectric domains
with both out-of-plane and in-plane net polarization (red arrows). Application
of a transverse electric field (here in [01$\bar{1}$] direction) forces the
polarization of out-of-plane domains to switch along the direction of the
applied electric field. In our case, the electric field is applied along
[01$\bar{1}$] crystal axis resulting in the sizable lattice deformation during
the ferroelastic transition which generates a tensile strain in this direction
(Fig. 1(e)). The strain is transferred through the ferroelectric/ferromagnetic
interface to the PSV structure and induces modifications of its static
magnetic properties due to the inverse magnetostrictive (magnetoelastic)
effect.

The MR loops of the Co/Cu/Py PSV tri-layer are investigated for the magnetic
field $H$ applied parallel to the probing current $I$ and under different
electric fields applied to the ferroelectric PMN–PT substrate (Fig. 2(a)). At
zero electric field (black graph), MR value reaches $\sim$2 $\%$, and the
shape of the loop indicates the sharp and separate switching of both Py and Co
magnetic layers with the switching fields $H_{sw}^{Py}\approx$ 15 Oe and
$H_{sw}^{Co}\approx$ 45 Oe respectively. Here, we define the switching field
as the onset magnetic field where the peak MR value at the plateau starts
decreasing from its maximum value. These values are in good agreement with the
switching process in the reference sample grown on Si/SiO2 substrate (see Fig.
2(b)). Slight deviations in the MR ratio and the switching field values may
arise due to small interface strains during the deposition or different PMN–PT
surface roughness as compared to Si/SiO2. When the lateral electric field is
applied to the substrate, the shape of the MR curves is notably modified (see
red and blue graphs in Fig. 2(a)). Upon increasing electric field, we can
distinct three superimposed effects: i) narrowing of the plateau between the
switching fields $H_{sw}^{Py}$ and $H_{sw}^{Py}$; ii) increase of the MR peak
steepness and iii) decrease of the GMR ratio of the PSV. The observed
narrowing of the plateau between the switching fields of the magnetic layers
comparing to the initial state originates from the decrease of the Co layer
switching field $H_{sw}^{Co}$. Fig. 2(b) shows both positive and negative
values of the switching fields of Co and Py magnetic layers vs. applied
electric field extracted from the corresponding MR loops. There is only
marginal impact of the electric field on the switching field of the Py layer,
whereas a monotonous decrease of the switching field of the Co layer is
observed when increasing the electric field. A gradual increase of the MR peak
steepness with increasing electric field (see Fig. 2(a)) indicates the
magnetic hardening of the $x$-axis of the stripe.

Figure 2: (a) Magnetoresistance loops of Co(5)/Cu(4.5)/Py(5) PSV stripe on
PMN–PT measured for different lateral electric fields applied to the
substrate. (b) Switching fields of Co (red squares) and Py (green circles)
layers extracted from (a).

The described effects are explained as a result of the strain-dependent
magnetic anisotropy in ferroelectric/ferromagnetic heterostructures. When a
lateral electric field is applied to the ferroelectric crystal in a
spontaneous ferroelectric state, the converse piezoelectric effect results in
an in-plane strain (see Fig. 1(e)). This strain, when transferred to the PSV
tri-layer, modifies the magnetic anisotropies of the magnetic layers via the
inverse magnetostrictive (magnetoelastic) effect. Both Co and Py magnetic
layers acquire an additional strain-dependent magnetoelastic energy
$E_{\sigma}=-\frac{3}{2}\lambda_{s}Y\epsilon cos^{2}\theta$ , where
$\lambda_{s}$ is the magnetostriction constant, $Y$ is the Young’s modulus of
the magnetic material, $\epsilon$ is the generated stress and $\theta$ is the
angle between the magnetization and strain directions. Given the close-to-zero
value of the magnetostriction constant of the Py compound Reekstin (1967), the
corresponding magnetoelastic contribution under strain is marginal and,
therefore, insufficient to induce any noticeable change in the magnetic
anisotropy of the Py layer. Therefore, the switching field $H_{sw}^{Py}$ of
the Py layer does not change significantly with increasing the electrically
induced strain in the structure. On the other hand, the inverse
magnetostrictive effect introduces a sizable magnetoelastic energy
contribution to the magnetic anisotropy of the Co layer, which depends on the
value of the electric-field-induced strain and on the magnetostriction
constant of Co. Since polycrystalline Co thin films have negative
magnetostriction constant Klokholm and Aboaf (1982), the tensile strain along
y-axis (see Fig. 1(a)) introduces an additional magnetoelastic anisotropy
along the transverse direction (here $x$-direction), making the $x$-axis more
preferable for the magnetization arrangement. This manifests in the decrease
of the switching field $H_{sw}^{Co}$ along the $x$-axis of the Co layer. This
explanation is also consistent with the gradual change of the shape of the MR
curves upon increasing strain, from the square-shaped easy-axis loop at 0 MV/m
to the triangular-shaped hard-axis loop at 2.4 MV/m (see Fig 2(a)).

Figure 3: (a) Giant magnetoresistance ratio values extracted from Fig. 2(a) as
a function of the applied electric field. (b) Angle between Co and Py net
magnetizations at zero magnetic field as a function of the applied electric
field. Red and green arrows denote the schematic orientation of the Co and Py
magnetizations at zero magnetic field.

Now we comment on the GMR ratio dependence on the applied electric field (Fig.
3(a)). The GMR ratio decrease is consistent with the strain-induced magnetic
anisotropy of the Co layer, resulting in the deviation of the Co magnetization
from its initial direction through a coherent magnetization rotation towards
the tensile strain direction (here $y$-axis). At the MR maximum and upon
increasing electric field, the angle between the magnetizations of Co and Py
layers decreases (as compared to the initial close-to-antiparallel state),
which therefore reduces the GMR ratio. On the other hand, at zero magnetic
field, the angle between the magnetization directions of Co and Py layers
increases with increasing the electrically induced strain (Fig. 2(a)). Fig.
3(b) shows the angle $\theta$ between the Co and Py net magnetizations as a
function of the electric field, and calculated based on the zero magnetic
field MR values of Fig. 2(a) using the relation
$R(\theta)=R_{P}+(R_{AP}-R_{P})\frac{1-cos\theta}{2}$ Dieny  _et al._ (1991) ,
where $R_{P}$ ($R_{AP}$) is the resistance in parallel (antiparallel) state. A
monotonous increase of this angle suggests that the electric field induced
change of the GMR ratio originates from the modification of the relative
orientation of the Co and Py magnetizations. Since the Py layer is insensitive
to strain (given its close-to-zero magnetostriction constant), we can
associate this increase of the angle $\theta$ to the rotation of the Co layer
magnetization only.

Figure 4: Magnetoresistance loops of Co(3.7)/Cu(4.5)/Py(5) stripe on Si
substrate measured for the different strains generated via the mechanical
bending of the substrate. The values of the strain were estimated from the
curvature of the sample support (see suppl. data for more details).

The strain-related origin of the observed effects is confirmed by a control
experiment where the MR of the Co/Cu/Py PSV fabricated on a (100)Si substrate
was measured as a function of the mechanical strain generated by bending the
substrate (see details in suppl. data). Fig. 4 shows the two-point MR
measurements performed on the Co(3.7)/Cu(4.5)/Py(5) PSV grown on (100)Si
substrate for $H\parallel I$ as a function of the tensile strain generated in
the direction transverse to the applied magnetic field. The unstrained sample
exhibits the MR ratio of about 1.1 $\%$ and the well-defined plateau between
the switching fields $H_{sw}^{Py}\approx$ 14 Oe and $H_{sw}^{Co}\approx$ 40
Oe. The tensile uniaxial strain, generated along the $y$-direction and
transverse to the MR probing direction (see inset of Fig. 4), leads to the
modification of the MR properties of the PSV. The MR loops measured under
strain exhibit narrower high-resistance plateaus with the decreased switching
field of the Co layer whereas the switching field of the Py layer remains
nearly unchanged. Similarly to the described above, this effect refers to the
increase of the Co film anisotropy along the $y$-direction due to the
increased magnetoelastic energy contribution introduced by the deformation of
the substrate. The magnetic anisotropy of the Py layer is marginally affected
by the strain due to the near-zero magnetostriction of the Py film. The
observed behaviour qualitatively reproduces the results obtained for PMN-
PT/Co/Cu/Py PSV described above, thus confirming the strain-related origin of
the observed effects on the switching fields of the magnetostrictive Co layer.

Contrary to the case of ferroelectric PMN-PT substrate, a slight increase of
the MR ratio is observed, which may be attributed to the enhanced spin-
dependent electron scattering through the Cu spacer or to the modified energy
landscape of the Co/Cu/Py tri-layer subjected to the complex deformation
(including non-uniform bending) rather than to a simple in-plane biaxial
strain.

Finally, we comment on the perspectives of the strain-controlled magnetic
anisotropy and magnetotransport in magnetostrictive ferromagnetic components
for applications in emerging micro- and nanoscale magnetic devices. A proper
selection of the geometry and materials comprising the magnetic multilayers is
a keystone of improving the efficiency of the strain-tunable magnetic
elements, which may potentially be integrated in the strain-controlled
spintronic sensors or memory devices Wang  _et al._ (2017, 2018). Moreover,
properly adjusted magnetostrictive properties of the constituent magnetic
layers enable a realization of a strain-mediated switch between quantum (GMR)
and classical (AMR) magnetotransport effects. Importantly, the lateral control
also helps avoiding charge injection issues, common for devices with vertical
electrical access, where the voltage is applied across the thickness of the
magnetic element. In addition, lateral electric-field creates a room for a
direct vertical access to the device for other types of excitation, e.g. light
illumination or irradiation by ion beams.

As another example, when applied to spin-torque nano-oscillators, the reported
effects may be used for controlling the spin polarization direction of the
polarizing layer or the magnetic anisotropy of the free layer, which may
broaden the dynamical range of such devices. Additionally, our findings may be
utilized for controlling the dynamical coupling between the magnetic layers in
magnetostrictive/non-magnetostrictive structures for efficient multilayer-
based spintronic oscillators Iurchuk  _et al._ (2021). As shown by the control
experiment, the origin of strain needed for the magnetization tuning is not
restricted to the converse piezoelectricity; therefore, the proposed concept
can be effectively implemented in any system regardless the strain generation
method. For example, recently demonstrated optically induced tuning of
magnetic properties by photostriction Kundys  _et al._ (2012); Iurchuk  _et
al._ (2016) may provide a new method of light-induced magnetic switching via
strain-mediated mechanism.

In summary, we have demonstrated the lateral electric field induced strain-
mediated control of giant magnetoresistance in PMN–PT/Co/Cu/Py pseudo spin
valve. We showed that the GMR ratio and the magnetization reversal process are
modified due to different magnetostrictive properties of the magnetic layers
comprising the PSV. In particular, the magnetic anisotropy of the Co layer can
be effectively tuned by the piezoelectric strain generated by a ferroelectric
substrate, while keeping the Py layer anisotropy unaffected. This result
provides an understanding of the necessity to take into account the difference
in magnetostrictive properties of the magnetic films while designing strain-
controllable layered magnetic systems.

## Supplementary material

See supplementary material for the details on the mechanical strain generation
using convex-shaped sample supports.

## Acknowledgments

The authors gratefully acknowledge the support of the French National Research
Agency via hvSTRICTSPIN ANR-13-JS 04-0008-01, Labex NIE 11-LABX-0058-NIE and
ANR-10-IDEX-0002-02 research grants.

## Data availability statement

The data that support the findings of this study are available from the
corresponding author upon reasonable request.

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