Magnetic viscosity in a nanocrystalline two phase composite with enhanced remanence

The intrinsic values of the magnetic viscosity and the fluctuation held in a two phase composite Nd2Fe14B + 0.18 vol. alpha Fe were investigated. The composite studied, with equiaxed and isotropically oriented grains had mean grain sizes favoring a strong exchange coupling between the phases. The re lations between the intrinsic and the experimentally measured magnitudes ar e reviewed and the approximations discussed. For applied fields close to th e coercivity, the time dependence of the magnetization is not well describe d by a simple logarithmic law. The intrinsic fluctuation held is found to i ncrease when the reverse internal field increases in all the ranges investi gated and two different regimes are identified. These different regimes are discussed considering the distributions of critical fields for nucleation of inverse domains in the hard phase, at hard-soft and hard-hard grain boun daries, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.