Restoration of ion beam irradiation induced metastable magnetic states and lattice structures of FeRh thin films by heat treatments at elevated temperatures

Abstract

The restoration process of irradiation-induced metastable magnetic states of FeRh thin films during the heat treatments at 373–1073 K was investigated by measuring the magnetization-magnetic field (M−H) curves and the magnetization-temperature (M−T) curves for the FeRh thin films irradiated with 50 keV Ar ions to various fluences. The recovery of lattice structures accompanying the magnetic restoration was also examined by an x-ray diffraction (XRD) measurement. For the ferromagnetic state induced by low fluence irradiation, the magnetic restoration to the thermal equilibrium antiferromagnetic state occurs during the heat treatment. Whereas for the paramagnetic state induced by high fluence irradiation, it once changes to the ferromagnetic state, and then, is restored to the antiferromagnetic (i.e., thermal equilibrium) state during the heat treatment. The above magnetic transformation occurs by the heat treatments at higher temperatures for the higher fluence irradiation. Moreover, the magnetic transition temperature from the antiferromagnetic state, which has been thermally restored from the irradiation induced ferromagnetic or paramagnetic state, to the ferromagnetic state decreases with increasing the irradiation fluence. This result implies that the antiferromagnetic state with larger amount of lattice defects is more unstable against the thermal vibration of lattice atoms.