A Comparison of the Losses for Domain-Wall Motion and Ferromagnetic Resonance in Thin Ni-Fe Alloy Films

Abstract

The connection between the losses for domain-wall motion and ferromagnetic resonance in Ni-Fe thin films has been investigated by examining the thickness dependence and temperature dependence of the wall mobility and the linewidth for resonance with the static magnetic field in the plane of the film. The losses at room temperature were compared in terms of Landau-Lifshitz damping parameters for the two processes. The wall-motion damping is approximately equal to 0.014 independent of thickness while the resonance damping increases from 0.005 at 200 Å to 0.010 at 3000 Å. In view of the large differences in damping for wall motion and resonance at 300°K, the relaxation mechanism (s) which contribute to the losses at 300°K in each case must be quite different. The losses as a function of temperature have been compared on the basis of changes in linewidth and mobility between 300°K and 77°K. The linewidth for films is known to exhibit a peak at about 77°K. The wall mobility at 300°K and 77°K has been obtained from Kerr observations (300°K) and flux reversal measurements (300°K and 77°K) for films 150 to 1350 Å thick which exhibited, to varying degrees, the above linewidth peak. A strong correlation between linewidth increase and mobility decrease from 300°K to 77°K was observed. The largest mobility decrease observed was from 1.7×104 to 8×103 cm/sec·Oe for a particular 150-Å film which exhibited a linewidth increase of 15 Oe (from 10 to 25 Oe at 4 Gc/sec). The increase in the losses for wall motion was directly related to the increase in the losses for resonance from 300°K to 77°K. The relaxation processes which contribute to the temperature dependence of the resonance linewidth are important in limiting domain-wall motion in Ni-Fe alloy films.