the present invention provides a method for fabricating a bottom spin - valve sensor element of high magnetoresistive ratio by forming a novel , specularly reflecting nano - oxide layer within its pinned layer . referring first to fig1 a , there is shown a schematic cross - sectional view of a typical prior art configuration of a bottom spin - filter element stack having a synthetic antiferromagnetically pinned ( syap ) layer . compositionally , said stack has the form : as shown in fig1 a , the stack comprises an nicr a seed layer ( 2 ) of approximately 40 angstroms thickness , an mnpt antiferromagnetic pinning layer ( 4 ) of approximately 130 angstroms thickness , a tri - layer formation of cofe / ru / cofe ( 6 ), which is a synthetic pinned layer formed of two cofe ferromagnetic layers ( 8 ) and ( 10 ), exchange coupled in mutually antiparallel magnetization directions through a ru coupling layer ( 12 ) of approximately 8 angstroms thickness . cofe layer ( 8 ) is denoted the second antiparallel layer , ap2 , and is formed to a thickness of approximately 15 angstroms . cofe layer ( 10 ) is denoted the first antiparallel layer , ap1 , and is formed to a thickness of approximately 20 angstroms . the term “ antiparallel ” in this context refers to the mutually antiparallel directions of the magnetizations of the two pinned layers that corresponds to the low energy state between ap 1 and ap2 when separated by a ru layer of approximately 8 a . the “ second ” layer referred to in this context is the one contiguous with the antiferromagnetic pinning layer ( 4 ), whereas the “ first ” layer ( 10 ) is the one contiguous with the subsequently deposited cu spacer layer ( 14 ). said cu spacer layer ( 14 ) is a non - magnetic spacer layer separating the pinned layer ( 6 ) from the free ferromagnetic layer ( 16 ), which is a cofe layer deposited to a thickness of approximately 20 angstroms . a cu layer ( 18 ) of approximate thickness 5 angstroms is formed on the free layer and a ta layer ( 20 ) of approximate thickness 8 angstroms is formed on the cu layer . layers ( 18 ) and ( 20 ) provide a capping formation for the sensor stack . referring next to fig1 b , there is shown a schematic cross - sectional view of the new structure , compositionally described below , formed in accord with the method of the present invention . 40a nicr / 130a mnpt / 15a cofe / 8a ru / 3a cofe / 5a feta // ox // 20a cofe / 21a cu / 20a cofe / 5a cu / 8a ta . as is shown schematically in fig1 b , the stack comprises an nicr ( or nifecr ) seed layer ( 2 ) of approximately 40 angstroms thickness on which is formed an mnpt antiferromagnetic pinning layer ( 4 ) of approximately 130 angstroms thickness . in accord with the present invention , the syap is now formed as five layered laminate ( 30 ), comprising a second antiparallel ( ap2 ) cofe ferromagnetic layer ( 6 ) formed to a thickness of approximately 15 angstroms , on which is formed a non - magnetic ru coupling layer ( 10 ) of approximately 8 angstroms thickness on which is formed a tri - layered first antiparallel ( ap1 ) layer ( 15 ). the ap1 and ap2 terminology is the same as that used in describing fig1 a . the ap1 layer ( 15 ), which in the prior art is a single cofe layer ( see layer ( 10 ) in fig1 a ), is now formed as a tri - layer , comprising a layer of cofe ( 17 ) of approximately 3 angstroms thickness , to maintain strong magnetic coupling between ap1 / ap2 since cofe / ru / feta coupling is weak , on which cofe layer is then formed a specularly reflecting fetao layer ( 19 ) of approximately 5 angstroms thickness , on which is formed a layer of cofe ( 21 ) of approximately 20 angstroms thickness . the fetao layer is formed as a deposited feta layer which is approximately 95 % fe by atomic weight and approximately 5 % ta by atomic weight , which is subsequently oxidized in either of the following processes in a pm5 tim module . ox1 : 50 sccm o 2 flow rate ( 0 . 5 mtorr )× 10 sec . ox2 : 75 sccm o 2 flow rate ( 0 . 75 mtorr )× 10 sec . ox3 : 100 seem o 2 flow rate ( 1 . 0 mtorr )× 10 sec . subsequent to the oxidation of the cofe layer ( 21 ), there is formed a non - magnetic spacer layer ( 14 ), which is a layer of cu formed to a thickness of approximately 21 angstroms and which separates the syap layer from the ferromagnetic free layer . that ferromagnetic free layer ( 16 ) is then formed on the cu spacer layer as a layer of cofe of approximately 20 angstroms thickness . upon said free layer there is then formed a cu oxidation barrier layer ( 18 ) of approximately 5 angstroms thickness , upon which is then formed a specular scattering layer ta layer ( 20 ) of approximately 8 angstroms thickness . although serving different purposes , the cu / ta layer is denoted a capping layer . subsequent to the formation of the element as above , the magnetizations of the various layers are established through a three step thermal anneal in the presence of external magnetic fields as follows : 1 : 270 ° c ./ 1 koe / 10 min ., for the free layer , the field being longitudinally directed . 2 : 270 ° c ./ 8 koe / 3 hr ., for the pinned layer , with the field being in the transverse direction . 3 : 210 ° c ./ 200 oe / 2 hr ., for the free layer , the field being longitudinally directed . experiments performed on sensor stacks formed in accord with the methods of the prior art and on sensor stacks formed in accord with the method of the present invention show a distinct improvement in the magnetoresistive properties of the latter stacks as compared with the former . table 1 below compares dr / r and dr for a reference prior art stack ( row 1 ) and stacks formed using the method of the present invention for each of the three oxidation processes described above ( rows 2 , 3 , 4 respectively ). all numerical values in the stack formations above are in angstroms . it can be seen from the experimental results that the enhancement of dr / r and dr is a maximum of 14 % and 21 % respectively for the ox2 sample . testing of hysteresis loops for the above samples also shows that the loops of the fetao samples are comparable to those of the reference samples indicating that sensor stacks formed in accord with the method of the present invention display strong coupling between the pinned and pinning layers . experimental and theoretical considerations lead us to conclude that the dr / r and dr improvements are a result of the improved specular reflection of conduction electrons provided by the fetao layer in the ap1 layer of the pinned layer . as is understood by a person skilled in the art , the preferred embodiment of the present invention is illustrative of the present invention rather than limiting of the present invention . revisions and modifications may be made to methods , materials , structures and dimensions employed in practicing the method of the present invention , while still remaining in accord with the spirit and scope of the present invention as defined by the appended claims .