Effect of Cold Rolling on Magnetization Reversal of High‐Purity Nickel Tapes

摘要

Dynamic magnetoresistance hysteresis loops were used for investigation of the magnetization reversal in cold‐rolled tapes of high‐purity nickel. The tapes were prepared by unidirectional rolling as well as by rolling with reversing tape end for end between passes. The loops were cycled in the range ±4500 Oe with a variety of frequencies f from 0.005 to 0.1 cps in the wide interval of temperatures from 297° to 4.2°K. When the magnetization field was transverse to the rolling axis, the coercive force could be expressed by Hc = A (lnf-lnf0)/T½, where A and f0 are in general dependent on the reduction of the tape thickness, and vary slightly with the temperature T. Such a relation may be related to a magnetization reversal occuring through a process of reorientation of spins, which can be described as a temperature‐activated domain‐wall relaxation. The magnetoresistance loops of the samples made by unidirectional cold rolling were asymmetric when they were performed by applying simultaneously two crossed magnetic fields, one ac and the other dc. A magnetic uniaxial anisotropy induced by this rolling seems to be responsible for the observed asymmetry, a possible mechanism for this being the deformation of crystals by slips.