Ferromagnetic resonance line width in magnetic films as a function of temperature

Abstract

Ferromagnetic resonance (FMR) experiment is considered for the case of a constant field applied in plane of a thin film. Role of temperature is investigated by replacing the Landau-Lifshitz-Gilbert equation by the Landau-Lifshitz-Bloch approach. Two important FMR parameters are evaluated: the resonance field and the line width. Although the resonant field has to be calculated numerically, a well working approximating expression is given. In the case of the line width, an analytical formula is obtained. Both the resonance field and the line width grow exponentially with temperature in the whole temperature range. The magnitude of the FMR line broadening is estimated by checking different conditions (microwave frequency and damping) for permalloy showing that increase of temperature from 0% to 90% of the Curie temperature increases the line width roughly by a factor of two.