The first order antiferromagnetic to ferromagnetic metamagnetic phase transition of equiatomic FeRh offers new opportunities for novel antiferromagnetic memories and spintronic devices with the caveat that it can be utilized in thin film structures (<50 nm). Here, we report a polarized neutron reflectivity (PNR) study for three representative film thicknesses (5, 20, and 50 nm) aimed at determining the physical and magnetic structure of FeRh at room temperature and partway through the transition. The PNR results are analyzed with reference to X-ray diffraction, X-ray reflectivity, and atomic force microscopy data which together provide a consistent description of the magnetic and physical state of the FeRh thin films. The data demonstrate that the nucleation of the ferromagnetic phase initiates at the MgO substrate, and results from structural and magnetic measurements demonstrate that the magnetic behavior and strain properties of FeRh correlate with the evolving topography of the three films investigated.
