AC losses in grain oriented Tb0.3Dy0.7Fe1.95

The complex permeability as a function of frequency has been investigated in grain-oriented Tb_0.3Dy_0.7Fe_1.95. Domain-wall effects increase the eddy-current losses in small applied (DC) fields, but with fields large enough to obtain optimum magnetomechanical coupling (k ₃₃), the losses agree with the theory for macroscopic eddy currents. The data provide an indication of the inherent bandwidth limitations of devices incorporating this material and are also relevant to the correction of dynamic k₃₃ measurements determined by the resonance-antiresonance technique. It is pointed out that a reliable scaling of dynamic k₃₃ data according to change in permeability with frequency is hampered by the rate of change of permeability in the range 1 to 10 kHz, and this difficulty demonstrates the need for a frequency-dependent loss mechanism to be included in the analysis of the resonance-antiresonance characteristics