Anisotropy in Rolled Permalloy Tape

Abstract

The anisotropy induced in gold-doped Permalloy by cold rolling and subsequent heat treatments has been investigated using a recording torque magnetometer. The material was cold rolled from 0.014 in. to 0.000125 in. and then heat treated for 2 hr in a dry hydrogen atmosphere. The torque curves obtained could be decomposed into a hard and soft component. For fields below 200 oe, the torque curves due to the hard component have a tangent-like shape with the peak a few degrees from the hard direction, while the torque curves due to the soft component have the regular shape corresponding to uniaxial magnetocrystalline anisotropy. Both components are uniaxial with the easy direction along the roll direction. The hard component is independent of the heat treatments up to about 900°C and has an equivalent anisotropy field of the order of several hundred oersteds. The high apparent anisotropy of the hard component and its independence of the heat treatment suggest that this component arises from a magnetostatic effect. By etching the tape it has been shown that the hard component is due to the surface structure of the tape. The surface structure is probably the result of the rolling process. The soft component is strongly dependent upon the heat treatment subsequent to the cold work and almost vanishes at an annealing temperature of about 650°C. This decrease is consistent with the ordered pair mechanism suggested by Chikazumi. The small residual soft component at high annealing temperatures is very sensitive to the rate of quenching. This behavior may indicate the presence of partial ordering and some degree of crystal orientation. The value of the anisotropy field due to the soft component is approximately equal to the measured value of the threshold for rapid rotational flux reversal.