Temperature and Mode Dependence of Ferromagnetic Thin Film Resonance Linewidths in the Range 4°–300°K

Abstract

The perpendicular resonance linewidths of the standing spin-wave modes in permalloy thin films have been measured as a function of the temperature and the mode number in the temperature range 4°–300°K. It is found that the linewidths obey the relation ΔH(T) = ΔH(0) [1—aT3/2], where ΔH(0) is the linewidth at absolute zero. Various two magnon relaxation calculations predict a linewidth that depends on the magnetization as ΔH∼Mq∼M(0) q[1-−qcT3/2] where c is the Bloch constant. The theoretical results for q are strongly model dependent, and published results to date predict q to be either mode independent or increasing slightly with increasing mode number. Experimental values obtained at 9.2 GHz have a value of q that ranges from about 3.3 for the main resonance mode (n=0) and decrease regularly to about 1.6 for the low-field mode as the mode numbers increase. Data at 9.2 and 23.8 GHz indicate there may be a slight frequency dependence to the q values. The data indicate that a two magnon scattering process is the most significant contribution to the linewidth in thin ferromagnetic films. It is suggested that the two magnon scattering process induced by an inhomogeneity in the internal field can produce the observed temperature dependence.