Origin of giant magnetoresistance in conventional AlNiCo5 magnets

Structure-property relationships in AlNiCo5 permanent magnets in the optimu m magnetic state have been investigated so as to uncover the origin of gian t magnetoresistance (GMR). According to analytical field ion and convention al transmission electron microscopy, AlNiCo5 consists of two coherent B2-or dered phases. One, alpha (1), corresponds to Fe7Co3 and the other, alpha (2 ), to Al1.1Ni0.9 with some substitution of Al, Ni, Cn and Fe, Co, Cu, respe ctively. Seventy percent of the GMR-effect can be attributed to superparama gnetic clusters, about 1 nm in size, positioned on the Al-rich alpha (2)-su blattice. The remaining 30% result from 3-6 nm superparamagnetic alpha (1)- clusters in the form of fine bridges interconnecting large alpha (1)-partic les normal to, or inclined to their direction of elongation. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.