Dynamic M-H loop study of energy losses in thin Ni-Fe films

Abstract

Dynamic energy losses in thin Ni-Fe films during magnetization reversal under sinusoidal magnetic drive fields of 15-Oe peak at frequencies up to 50 kHz have been studied by direct observation of the dynamic M-H loop. Empirically it is found that the energy losses depend neither upon frequency alone nor peak drive fieId alone, but rather upon the slope S in Oe/s of the drive field at the instant of magnetization reversal. Energy losses are proportional to (S)^{1/2} for small S and to S for large S up to S = 5 \times 10^{6} Oe/s, the apparatus limit. Simultaneous observation of easy-axis and hard-axis pick-up loop voltage waveforms indicates that magnetization reversal occurs by coherent rotation for large S and by domain-wall motion for small S . Observed behavior of the energy losses is shown to be in conformity with the classical descriptions of domain-wall motion and coherent rotation.