[16p-D419-1~18] 10.2 Fundamental and exploratory device technologies for spin

▲ [16p-D419-5] Low Gilbert damping and damping anisotropy in Fe_xCo_1-x alloys films

〇Zaizhou Jin^1,2, Mandal Mandal², Shigemi Mizukami^2,3 (1.Tohoku Univ., 2.AIMR,Tohoku Univ., 3.CSIS,Tohoku Univ.)

Keywords:spintronics, spin dynamics

Magnetic Gilbert damping determines how fast the magnetization relaxes toward the effective magnetic field and plays a central role in spintronics devices. Recently Yi Li et al. observed giant damping anisotropy in FeCo. However, there is still a large gap between theoretical calculations and experiments. In this study, we investigate Gilbert damping in the epitaxial FexCo1-x alloy films with different alloy concentrations and different thicknesses using a broadband ferromagnetic resonance (FMR) spectrometer. A series of Fe1-xCox films with different thicknesses (7, 20, 25, and 50 nm) were deposited at room temperature either on (100) MgO or MgAl2O4 (MAO) single crystalline substrates using a magnetron sputtering. The nominal composition x was varied using co-sputtering techniques. Film crystalline structures were evaluated using X-ray diffraction (XRD). Magnetization measurements were performed using vibrating sample magnetometer (VSM). FMR measurements were performed using vector-network analyzer (VNA) with frequencies up to about 20 GHz.
XRD measurements confirmed the epitaxial growth for all the films with the epitaxial relationship of MgO(001)<100>//Fe1-xCox(001)<110>. Figure 1 shows the Gilbert damping constant evaluated from the slope of the linewidth vs. frequency data. The damping value shows large anisotropy for the crystalline axis; the maximum damping anisotropy, about 300%, is found in 7 nm Fe75Co25/MgO. In addition, we also observed a clear substrate dependence of damping, which may be related to the stress state and crystal quality. In the presentation, we will show the thickness and composition dependence of damping anisotropy, and discuss their physical origin.