Temperature dependence of stress-anneal-induced anisotropy in nanocrystalline magnets

Abstract
It has recently been shown that the anisotropy in nanocrystalline FINEMET-type magnets, induced by their crystallization under tensile stress, can originate from the magnetoelastic coupling within the crystallites or can have its source in directional diatomic ordering which occurs also within the volume of nanocrystalline phase in the present work the temperature dependence of this anisotropy has been investigated for a series of initially amorphous Fe_73,5Cu₃Nb₃Si_15,2B₇-ribbon samples (Vacuumschmelze, GmbH), nanocrystallized at various temperature-time-stress conditions. It has been assumed that the obtained results will allow to judge which of the mechanisms mentional above governs in reality the considered anisotropy. An analysis of the results obtained show that diatomic directional ordering within the volume of the nanocrystalline phase seems to be very likely the origin of the stress-anneal-induced anisotropy in Finemet-type magnets. This analysis has been performed assuming that the anisotropy originating from the atomic ordering should scale with the square of saturation magnetization in the high temperature range (in the vicinity of critical temperature - Curie point of the nanocrystalline phase) and with the cube of this quantity at low temperatures. Quite satisfactory agreement has been obtained for the best fit of the experimental data to the polynomial consisting of the two above terms.