Magnetic aftereffect in textured Ni/Cu compositionally modulated alloys (abstract)

Abstract

The existence of a magnetic aftereffect (‘‘magnetic viscosity’’) in textured Ni/Cu multilayered alloys was established1 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, though most often for systems composed of superparamagnetic particles, where the relaxation freezes out at low temperatures. In contrast, the relaxation is enhanced at low temperature in the present situation. Several questions remain open from this earlier work. Among these are: is the effect a property of a thin Ni film or is it attributable to the compositional modulation of the alloy?; what is the exact form of the time decay and what is the mechanism that causes this effect? In order to resolve some of these issues the magnetic aftereffect has been measured in more detail and for longer periods of time at both temperatures (room and 86 K) in a new set of [111]-textured, layered Cu/Ni alloys of varying thicknesses. The slab thickness of the Ni, dNi, was varied between 6 and 30 Å, and the ratio dNi/(dNi+dCu) between 0.1 and 0.8.