Fe Spin Reorientation across the Metamagnetic Transition in Strained FeRh Thin Films

A spin reorientation accompanying the temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) phase transition is reported in strained epitaxial FeRh thin films. ${}^{57}\mathrm{Fe}$ conversion electron Mössbauer spectrometry showed that the Fe moments have different orientations in FeRh grown on thick single-crystalline MgO and in FeRh grown on ion-beam-assist-deposited (IBAD) MgO. It was also observed, in both samples, that the Fe moments switch orientations at the AFM to FM phase transition. Perpendicular anisotropy was evidenced in the AFM phase of the film grown on IBAD MgO and in the FM phase of that grown on regular MgO. Density-functional theory calculations enabled this spin-reorientation transition to be accurately reproduced for both FeRh films across the AFM-FM phase transition and show that these results are due to differences in strain.

Figure 1

CEMS spectra obtained at different temperatures on (a,c) ${\mathrm{Fe}}_{0.98}{\mathrm{Rh}}_{1.02}//\mathrm{MgO}$ and (b),(d) ${\mathrm{Fe}}_{0.98}{\mathrm{Rh}}_{1.02}//\mathrm{IBAD}$ MgO. The room temperature spectra (a,b) correspond to the AFM phase and the high-temperature spectra (c),(d) to the FM phase. Note that (c) was obtained upon heating and (d) upon cooling.

Figure 2

Temperature dependence of the hyperfine field upon heating and cooling for (a) ${\mathrm{Fe}}_{0.98}{\mathrm{Rh}}_{1.02}//\mathrm{MgO}$ and (b) ${\mathrm{Fe}}_{0.98}{\mathrm{Rh}}_{1.02}//\mathrm{IBAD}$ MgO. Insets show the Fe moment orientation with respect to the sample plane in both AFM and FM phases for each sample. Temperature dependence of the magnetization (measured under 1 T and extrapolated in zero field using the experimental coefficient of $8\mathrm{K}/\mathrm{T}$) upon heating and cooling for (c) ${\mathrm{Fe}}_{0.98}{\mathrm{Rh}}_{1.02}//\mathrm{MgO}$ and (d) ${\mathrm{Fe}}_{0.98}{\mathrm{Rh}}_{1.02}//\mathrm{IBAD}$ MgO.

Figure 3

MCA energy calculated as a function of the $c/a$ ratio for each of the two magnetic phases.