Temperature-Induced Metamagnetic Transition and Domain Structures of Single-Crystalline FeRh Thin Films on MgO(100)

Exchange systems of FeRh with a hard magnetic layer are a promising approach for heat-assisted magnetic recording that can largely increase the storage density of hard disk drives. The FeRh alloy is known to undergo a temperature-induced metamagnetic transition from antiferromagnetic (AFM) to ferromagnetic (FM) just above the room temperature. But the AFM and FM phases coexist across the transition in single-crystalline FeRh thin lms with thin capping layers (e.g. Au, Al, or MgO). In order to investigate the intrinsic surface magnetic properties, single-crystalline FeRh films without capping layer are prepared by two kinds of experimental procedures. For the ex-situ sample preparation procedure, two 40nm thick, single-crystalline FeRh films are prepared on MgO(100) by separate layer deposition of Fe and Rh. X-ray photoemission spectroscopy (XPS) immediately after the deposition shows that one sample is Rh-rich and the other Fe-rich. The samples are exposed to air and transferred to a second ultra-high vacuum (UHV) system to perform the magnetic characterization. This transfer results in a contamination by C and O. After surface cleaning by high-temperature annealing the Rh-rich sample is still slightly contaminated with C, while the Fe-rich surface is oxidized. Magneto-optical Kerr effect (MOKE) measurements reveal that only the Rh-rich sample shows the metamagnetic transition below room temperature. The Fe-rich sample is FM at 193 and 293 K. Scanning electron microscopy with polarization analysis (SEMPA) reveals that the Rh-rich surface is FM at all temperatures between 160 and 450K although the bulk is AFM below room temperature. For the in-situ sample preparation procedure, a 10nm single-crystalline FeRh film is prepared on MgO(100) again by separate layer deposition of Fe and Rh but now in the same UHV system as all characterizations. Thus, the intrinsic properties of the single-crystalline FeRh film are investigated without exposure to air and additional cleaning steps. The in-situ prepared FeRh lm also exhibits the metamagnetic phase transition below room temperature as indicated by MOKE. The temperature dependent domain structure obtained by SEMPA reveals that FM domains exist at the surface while the bulk is AFM. In contrast to the ex-situ prepared sample the domain size changes drastically at the transition temperature. This is related to a spin reorientation transition from out-of-plane to in-plane between 350 to 400 K. The results show that the previously observed coexistence of the FM state at the surface and the AFM phase in the bulk is not due to an artifact of capping layers or surface contamination. This coexistence is shown in this work to be an intrinsic property of (100) surfaces of single-crystalline FeRh thin films on MgO(100)