Improved soft magnetic behaviour in field-annealed nanocrystalline Hitperm alloys

The effect of both longitudinal and transverse magnetic field applied during the heat treatment on the magnetic properties of HITPERM-type (Fe1-xCox)(81)Nb7B12 (x = 0.25,0.33,0.5,0.66,0.75) alloys has been investigated. The strongest response to the field annealing is found for the alloys with Fe/Co ratio close to the equiatomic composition (x = 0.5). After annealing in a transverse magnetic field, the induced anisotropies up to K-u similar to 1400J/m(3) have been obtained. A heat treatment under presence of longitudinal magnetic field results in squared hysteresis loops characterized by the coercive field values in the range 6-10 A/m. These H, values are superior to those previously reported for HITPERM materials and we show that they remain fairly stable also at elevated temperatures. The differences in the development of induced anisotropy in the series of alloys with varying Fe/Co ratio are discussed in the frame of the magnetic atoms pair ordering theory. (c) 2006 Elsevier B.V. All rights reserved.