with those of the corresponding $R$-metal [@Anderson-Nclr-Nd-Sm-DY-Schottky] and $R$Co$_{2}$B$_{2}$C isomorphs.[@Massalami-RCo2B2C]

Results and Analysis
====================

From the general feature of $C_{M}(T)$ curves (Figs.1-3,5-6), one distinguishes four temperature regions: (i) a paramagnetic region, $T>T_{N}$, wherein $C_{M}(T)$ is predominantly due to a change in the population of the CEF levels, (ii) a critical region, $T\approx T_{N}$, wherein $C_{M}(T)$ is related to the critical phenomena, (iii) an intermediate region wherein $C_{M}(T)$ reflects the magnetic character of the spiral/modulated states, and (iv) the low-temperature AF/squared-up states, of prime interest to this work, wherein the measured $C_{M}(T)$ is to be confronted with Eqs.\[Cm-bessel\],\[Cm-2d\] and therefrom $\ \theta$ and $\Delta$ are to be extracted.

Before we discuss the features of $C_{M}(T)$ for each compound, a word of caution is in order: just as in the case of $R$-metals,[@Coqblin-book] the propagation of errors due to successive subtraction of $C_{e}(T)$, $C_{D}(T)$ and $C_{N}(T)$ would eventually influence the absolute value of $C_{M}(T)$.

GdNi$_{2}$B$_{2}$C
------------------

Below $T_{N}$, the zero-field magnetic structure [@Detlefs-GdNi2B2C-XRES] is a transverse sine-modulated type with $\overrightarrow{k_{a}}$ that changes from 0.551$\overset{\ast}{a}$ at $T_{N}$ to 0.550$\overset{\ast}{a}$ at $T_{R}$, where a spin reorientation process sets-in. Below $T_{R}$, $\overrightarrow{k_{a}}$ reverts course and increases monotonically till reaching 0.553$\overset{\ast}{a}$ at 3.5 K.

$C_{M}(T)$ of 