Structural evidence for stabilized ferromagnetism in epitaxial FeRh nanoislands

Nanoislands of ??-FeRh were formed by the deposition of a 10?nm film onto (0?0?1)-MgO and observed by atomic force microscopy. This island-like architecture results in stabilized ferromagnetic (FM) ordering at low temperatures as noted by asymmetry in the x-ray diffraction peaks, a magnetostructural transition with a large magnetic background signal, and broad thermal hysteresis. The combination of structural and magnetic results suggest that the crystallographic arrangement of the FeRh nanoislands consists of a gradient of lattice parameters where there is a compressed inner region of lower lattice parameter values (attributed to antiferromagnetic ordering) which gradually relaxes outward to a region of larger lattice parameters (attributed to a retained FM ordering). The impact of this configuration on magnetostructural transformation is discussed in the context of classical nucleation theory.