Inverse giant magnetoresistance in granular Nd2Fe14 B/α-Fe

Partially amorphous Nd-Fe-B ribbons containing 20 or 50 wt% Fe in excess of the nominal composition Nd₂Fe₁₄B with 2.9 wt% Cu and 9.7 wt% Zr (referred to Nd₂Fe₁₄B) were prepared by melt-spinning. After a heat treatment the material consists of a mixture of three parts: hard magnetic grains of the Nd₂Fe₁₄B phase with α-Fe grains and, in the case of 20 wt% excess Fe, small amounts of a metastable cubic phase, Nd ₂Fe₂₃B₃. Samples with 20 wt% Fe show a superposition of anisotropic magnetoresistance and giant magnetoresistance (GMR) effects, depending on structural changes caused by heat treatments at various annealing temperatures. For measurements with the applied field both parallel and perpendicular to the sample current an isotropic positive magnetoresistance ratio, MR=[R(H)-R(0)]/R(0), called inverse GMR has been found for samples with 50 wt% excess Fe