Temperature dependence static and dynamic properties of soft magnetic thin film FeGaB/Al2O3 for microwave applications

Abstract

The recent reports on magnetodynamic properties of soft magnetic thin films attain the lowest damping factor [1-3]. The damping is required for spin-wave propagation and spin manipulation investigation where the reduced spin-wave dissipation leads to a larger decay length. The low damping thin films are important for microwave applications [4], spin transfer switching devices, and other application in magnon spintronics. In order to achieve the lowest damping, the FeGaB has chosen with Al2O3 in this study.Ta(10nm)/FeGaB(15nm)/Al2O3(3nm)/Ta(3nm) thin film were deposited on Si/SiO2(190nm) substrate by sputtering and was annealed at 300oC for 3 hours in the Ar gas. The static magnetization results inform that saturation and remanent magnetization has increased for annealed thin film shown in Fig.1 (a). After annealing, the dipolar field influence has reduced, the magnetic moment fluctuation has not observed. Fig. 1 (b) shows the annealed films have monotonously increased. The dynamics properties are studied with temperature variation with 100 K to 300 K and exciting frequency from 2 to 20 GHz. Fig.2 (a) illustrates the absorption spectrum of both films at 100K, the spectrum has shifted to lower fields for annealed films. The unannealed thin film have existed the small hump at higher magnetic films before resonance peak, which may be impurities and surface defects of the thin film. But, the hump has disappeared for annealed films in Fig. 2 (b). The absorption spectrum provides linewidth and resonance fields (Hr) for excitation frequency. The linewidth –frequency plot provides damping factor and inhomogeneous linewidth [5]. The damping factor of both films are decreasing with decreasing temperature as Fig.2 (c). Fig.2 (d) shows the annealed film has larger effective magnetization value than that of unannealed thin film.  Fig.1 (a) Normalized M-H loop for unannealed and annealed thin films at 300K. Insets shows M-H loop at different temperatures; (b) Coercive fields (Hc) versus temperature.  Fig.2 (a) Absorption spectrum of both thin films at 100K, (b) absorption of annealed thin film at 20GHz with different temperatures, (c) damping factor (α) versus temperature, (d) effective magnetization versus temperature.