Effect of site disorder on the resonant microwave absorption in Co2Fe0.5Ti0.5Si Heusler alloy thin films

Abstract

100 nm Co2Fe0.5Ti0.5Si (CFTS) thin films were grown on Si (100) substrate at different substrate temperatures TS to study the effect of site disorder on the magnetization relaxation processes and magnetic anisotropy in them. To this end, two different ferromagnetic resonance (FMR) techniques have been employed: broad-band (3 – 17 GHz) FMR at a fixed static magnetic field angle in the ‘in-plane’ (IP) sample geometry, and X-band (9.45 GHz) FMR at different polar field-angles, θH, in the ‘out-of-plane’ (OP) sample configuration. Increase in TS reduces the degree of disorder and improves crystalline order. Improvement in crystallinity, in turn, results in the decrease in the strength of magnetocrystalline anisotropy. Irrespective of the degree of disorder present, the OP anisotropy field, Hk⊥, is an order of magnitude higher than the IP counterpart, Hk‖. Out of the CFTS thin films studied, the film (TS500), deposited at TS = 500 °C, has the maximum L21 crystalline order, maximum saturation magnetization (MS = 779 G), and the least values for Hk‖ (5.3 Oe), Hk⊥ (17 Oe), Landé splitting factor, g = 2.02, and the Gilbert damping constant, α=5.5×10-3. These optimum values of MS, g and α, at room temperature, are conducive for spintronics applications. In the OP configuration, the FMR linewidth, ΔH⊥, mainly arises from the intrinsic Landau-Lifshitz-Gilbert damping and extrinsic angular spread of crystallite misorientation. However, the extrinsic two-magnon scattering contribution to ΔH⊥, is appreciable only in the angular range 70° ≤ θH ≤ 110° .