Spatially-resolved characterization of magnetic orderings and dynamics in hydrogen-ion-irradiated FeRh films

FeRh undergoes a magnetic phase transition around 380 K between antiferromagnetic (AFM) and ferromagnetic (FM) states accompanied by a structural change, and it exhibits a high flexibility in its magnetic properties when subject to various external factors, including pressure and laser pulses. In particular, the H-ion irradiation has been often adopted as an efficient way to better stabilize the FM state at the lower temperature below 300 K. By the way, the alteration of magnetic states by ion irradiation is achieved by a defect formation which is likely formed inhomogeneously due to a limited penetration depth of the ions. Therefore, it is important to examine the spatial distribution of magnetic states and also a possible deterioration of magnetic properties upon the H-ion irradiation. In this work, we addressed this issue by using both surface-specific and bulk-sensitive magneto-optical measurement techniques, and could reveal that the surface FM state can be stabilized together with the bulk AFM state within a single layer of FeRh. Furthermore, we found that the spin precessional dynamics including the damping factor remain relatively unchanged despite the high defect concentration induced by the high-dose H-ion irradiation. These findings provide an important step toward optimizing magnetic properties of FeRh films for their application in advanced spintronic devices.