The Study on Ferromagnetic Resonance Linewidth for NM/80NiFe/NM (NM=Cu, Ta, Pd and Pt) Films

Abstract

The out-of-plane angular dependence of ferromagnetic resonance (FMR) was measured for NM/80NiFe(Py)/NM (NM=Cu, Ta, Pd and Pt) films with various Py, Cu and Ta thicknesses fabricated by magnetron sputtering. The out-of-plane angular dependences of FMR resonance field and linewidth were analyzed using Landau-Lifshitz-Gilbert equation taking account of broadening of linewidth due to magnetic inhomogeneities in a film. Magnetic inhomogeneities were assumed to be the fluctuation of magnitude and direction of the effective demagnetization field which contains both demagnetization and perpendicular anisotropy field for a film. The calculations of the angular variations of linewidth agreed with the experimental ones quantitatively. The fluctuations of magnitude and direction of the effective demagnetization field, which are represented as Δ(4πM eff.) and Δθ H , respectively, increased with decreasing Py thickness for all NM/Py/NM films. Δθ H increased as the thicknesses of the buffer layers increased for Cu/Py(40 Å)/Cu films and was almost constant with increasing buffer layer thickness for Ta/Py(40 Å)/Ta films. Only in the case of NM=Pd and Pt films, the Gilbert damping parameter, which is the speed of decay of magnetization precession, was enhanced significantly as compared with that for the bulk sample and was dependent on Py thickness.

Enhanced Gilbert Damping in Thin Ferromagnetic Films

“…Enhancement of the damping constant a 0 a 2 a 0 can be expressed in terms of the scattering matrix at the Fermi energy of a ferromagnetic film in contact with normal metal reservoirs, which can be readily obtained by model or first-principles calculations. Our numerical estimates of a 0 compare well with recent experimental results [12]. Earlier experiments reported in Ref.…”

“…The damping is significant for transition metal films thinner than about 10 nm. Recent experiments on permalloy films [12] are well explained.…”

“…The factor 1͞d does not reflect an intrinsic effect; a reduced total magnetization is simply more sensitive to a given spin-current loss at the interface. Comparing with the intrinsic a 0 ഠ 0.006 of permalloy [12,21] the spin-current induced damping becomes important for ferromagnetic layers with thickness d , 100 Å. We can refine the estimate by including the significant film-thickness dependence of the magnetization measured by the same group [12].…”

“…Mizukami et al [12] measured the ferromagnetic resonance linewidth of N-Py-N sandwiches and discovered systematic trends in the damping parameter as a function of Py layer thickness d for different normal metals. The spin polarization of electrons emitted by Py has been measured to be p ഠ 0.4 in point contacts [19], the magnetization per atom is f ഠ 1.2, and the Landé factor is g L ഠ 2.1 [12]. The interface conductance of metallic interfaces with Fe or Co is of the order of 10 15 V 21 m 22 , with significant but not drastic dependences on interface morphology or material combination [20].…”

Spin pumping and inverse spin Hall voltages from dynamical antiferromagnets

“…In the biaxial NiO, the voltages are much weaker, and there is no spin-flop enhancement of the dc component. Spin pumping is a versatile tool for probing spin dynamics in ferromagnets [1][2][3][4][5][6]. The magnitude of the pumped spin currents reveals information about the magnetization dynamics and the electron-magnon coupling at interfaces [7][8][9].…”