Higher ferromagnetic resonance frequency in NiFe/FeMn film obtained by flash annealing in reversing field

Abstract

The unsaturated magnetization reversal by pulsed current annealing was investigated in exchange biased NiFe(15 nm)/FeMn(10 nm) bilayer. The magnetization reversal was conducted by energizing and thus heating the film under an external applied magnetic field ( $$H_{\text{a}}$$ ) with the direction opposite to the deposition field ( $$H_{\text{d}}$$ ). The static and dynamic magnetic properties of the films before and after rapid annealing were characterized using vibrating sample magnetometer, anisotropic magnetoresistance (AMR) and vector network analyzer measurements. When the samples were annealed at 40 and 45 V condenser voltages, greater values of rotational anisotropy $$(H_{\text{rot}} )$$ , ferromagnetic resonance frequency ( $$f_{\text{r}}$$ ) and smaller values of exchange bias field $$(H_{\text{e}} )$$ , exchange bias field in AMR measurement ( $$H_{\text{e}}^{\text{MR}}$$ ), and magnetoresistance in the samples were obtained, which is attributed to the unsaturated reversed magnetization in reversing magnetic field. A suggested model for which the scattered magnetization of magnetic moment results in additional unstable antiferromagnetic spins in the film was proposed to explain this interesting phenomenon.