Dipole-dipole interaction in superparamagnetic nanocrystalline Fe63.5Cr10Si13.5B9Cu1Nb3

Cr-substituted Finemet-type nanocrystalline alloy (Fe63.5Cr10Si13.5B9Cu1Nb3 ) has been studied by differential scanning calorimetry, x-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. The Curie temperature o f the remaining amorphous phase decreases as the crystalline volume fractio n increases, reaching values below room temperature. This feature makes the alloy adequate for studying the magnetic decoupling of the (Fe,Si) nanocry stals at moderated temperatures and, in particular, the superparamagnetic r elaxation in broad temperature and crystalline fraction ranges. It was show n that the anomalous dependence of the coercive field on the annealing temp erature can be satisfactorily explained assuming a dipolar-type interaction between the crystallites. (C) 2001 American Institute of Physics.