MAGNETIC VISCOSITY IN NI/CU COMPOSITIONALLY MODULATED ALLOYS

The existence of a magnetic aftereffect (magnetic viscosity) in Ni/Cu multilayered alloys was established using a vibrating sample magnetometer at room temperature and at 86 K. It was shown that the effect is strongly dependent on the step field H2 (i.e., the value the field is reduced to after the magnetic moment has been aligned in high field) and exhibits a maximum relaxation rate for values of H2 around the reverse coercive field -Hc. Aftereffect behavior of this type has been observed in other materials, although most often for systems composed of superparamagnetic particles, where the relaxation freezes out at low temperatures. In contrast, the relaxation in the CMA was shown to be enhanced at 86 K over its value at room temperature. New measurements over a wider temperature range show that the enhancement in this sample reaches a maximum near 120 K, but below that temperature the relaxation does freeze out. The temperature of maximum enhancement varies from sample to sample.