Effect of temperature on the ferromagnetic resonance of Ni 50Fe 50 thin films

Abstract

We report on the effect of temperature on the ferromagnetic resonance (FMR) spectra of Ni 50Fe 50 thin films sputtered on Si (0 0 1) wafers. The FMR field and linewidth were studied as a function of the ferromagnetic layer thickness t, and temperature T. The data are interpreted in the framework of a phenomenological model that includes in- and out-of-plane uniaxial anisotropy fields. The main effect of temperature on the magnetic properties of these films is to increase the in-plane uniaxial anisotropy and to induce a surface anisotropy that pushes the magnetization out-of-plane. The temperature dependence of the resonance field is explained assuming the magnetic anisotropies varying as m 3, where m = M ( T ) / M ( 0 ) is a reduce magnetization and M( T) follows the law (1− CTe −E/KT ), where E∝ T C is the energy gap of the spin wave spectrum, and T C being the Curie temperature. The resonance field as a function of temperature shows a transition temperature separating two different ferromagnetic regimes. At lower temperatures a new magnetic transition is observed in thinner films. The temperature dependence of the FMR linewidth departs from that expected in other transition metal structures at very low temperatures. This behavior is unique and may be associated with interface and surface effects.