Evolution of strain across the magnetostructural phase transition in epitaxial FeRh films on different substrates

Abstract

We present a detailed x-ray diffraction study of the structural evolution of epitaxial FeRh films across the temperature-driven phase transition between antiferromagnetic and ferromagnetic order. FeRh films grown onto MgO, W/MgO, and $\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$ substrates show qualitatively different lattice distortions (tetragonal vs rhombohedral), while keeping a sharp transition above room temperature. Temperature-dependent x-ray reciprocal space mapping reveals the phase-specific crystal structure, giving access to both in-plane and out-of-plane lattice parameters and crystalline coherence lengths across different stages of the phase transition. Diffuse x-ray scattering from relaxed films is treated via a mosaic block model, which provides a robust data fitting scheme. It is found that the ferromagnetic phase fraction can stand a larger amount of strain before completely annihilating and transitioning to the antiferromagnetic phase upon cooling, as compared to heating. This is related to the distinct magnetic exchange correlations in the antiferromagnetic and ferromagnetic parent phases.