Magnetostriction and angular dependence of ferromagnetic resonance linewidth in Tb-doped Ni0.8Fe0.2 thin films

Abstract

We present the dependence of the magnetostriction in Ni0.8Fe0.2 films on Tb and Gd doping concentration and compare with the measured doping dependence of the high-frequency damping. While the magnetostriction and the high-frequency damping are correlated, the dependence is complicated. In particular, the high-frequency damping parameter α increases rapidly (α=0.008–0.84) with a modest increase in the magnetostriction (λs=−0.6×10−6 to 5.7×10−6) for Tb doping concentrations up to 10%. For Gd doping, the high-frequency damping changes slowly (α=0.008–0.02) as the doping concentration is increased to 10%, whereas the increase in magnetostriction is similar to that observed in the Tb-doped films. Further, it is possible to achieve low magnetostriction (λs=2×10−6) near the region of critical damping. Measurements of the angular dependence of the ferromagnetic resonance linewidth in Tb-doped Ni0.8Fe0.2 films show little change similar to the behavior observed in undoped Ni0.8Fe0.2 films, although the linewidths are considerably larger. This is in contrast to systems such as Ni0.8Fe0.2 on NiO, which have a large angular dependence indicating that the relaxation process proceeds through the generation of spin waves. The enhanced damping in the Tb-doped films appears, therefore, to be mediated through direct phonon generation.