Applications using FeRh for controllable exchange coupling of two magnetic layers with in-plane
and out-of-plane anisotropies require ultrathin ( 10 nm) films with pure antiferromagnetic (AF)
FeRh a00 phase at room temperature (RT). However, it is also well known that the
antiferromagnetic-ferromagnetic (AF-FM) transition of FeRh is sensitive to composition and deteriorates
at low thicknesses. Hence, in this work, we study the composition-dependent phase ordering
of co-sputtered FeRh thin films at ultrathin thicknesses of 10 nm. As the ultrathin films get
richer in Rh, the appearance of a00 phase is typically characterized magnetically by a sudden drop
in RT moment, and structurally by a slight decrease in degree of B2 chemical ordering with a sharp
decrease in c-axis lattice constant. These observations are consistent with the FeRh phase diagram
where FeRh abruptly enters the AF a00 phase once it becomes slightly disordered. Dependences of
magnetic transition parameters on composition were also described. Moreover, higher sputtering
powers possibly allow the formation of purer a00 phase with less c-face centered cubic phase impurities.
Consequently, a composition optimized 10 nm film shows a relatively low residual moment
(13.5 emu/cc), thus suggesting good AF phase formation. In addition, correlation of the magnetic
transition parameters with the crystal structural parameters reveal that the maximum rate of
AF-FM transition (Rmax,h) and the corresponding total change in magnetization (DMh) interestingly
shows linear dependence on the c-axis lattice constant, but would depart from this linearity under
certain conditions, i.e., when grain sizes were large, crystallinity was improved and Fe content was
high.
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Copyright (2014) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in J. Appl. Phys. 116, 043902 (2014) and may be found at http://dx.doi.org/10.1063/1.4890032.