DYNAMIC KERR OBSERVATIONS OF HIGH SPEED FLUX REVERSAL AND RELAXATION PROCESSES IN PERMALLOY THIN FILMS

Sequences of dynamic Kerr photographs with 10 μ resolution have been taken during high-speed flux reversal and as the magnetization relaxes from a state of dynamic equilibrium to the final state of static equilibrium upon termination of the drive field. Equipment used consisted of a sampling Kerr magneto-optic camera with a Q-switched ruby laser for a light source. The 10 nsec exposure time was synchronized with a variable time delay between application of the magnetic field and actuation of the camera stable to within 3 nsec. The results show that, with zero transverse field, longitudinal propagation of diffuse transverse boundaries and nucleation of partially reversed regions are processes which are involved in intermediate and high-speed switching, respectively. The velocity of the diffuse boundary varies approximately as H5, and the mobility is as large as 1.4 cm/Oe-μsec. With a transverse field, the low-speed reversal is similar to diffuse boundary propagation and the higher-speed processes are rotational in nature. The transition from the propagational phenomenon to the rotational phenomenon is abrupt. Blocking is easily observable and is found to be important in the rotational process. Furthermore, it has been found that, if the reversing field is terminated prior to saturation, the flux either continues to reverse or relaxes to a less-switched condition, in times of the order of 1 μsec. Hence, conclusions drawn from interrupted pulse experiments may be in considerable error. A complete description of the results of this investigation will be published in the May, 1969 issue of the Journal of Applied Physics. © 1969 The American Institute of Physics.