Relation between structure and magnetic properties of Nd2(Fe, Co, Mo)14B/α-Fe nanocomposite magnets

The relationship between nanostructure, exchange coupling and magnetic properties of Nd-2(Fe, Co, Mo) B/alpha-Fe nanocomposite magnets prepared by mechanical alloying (MA) has been studied systematically. Different categories of grain interfaces have been directly observed, which correspond to different types of exchange couplings in the Nd2Fe14B/alpha-Fe-type nanocomposite magnets. The notable decrease of the spin-reorientation temperature T-sr of Nd2Fe14B phase convincingly demonstrates the presence of strong inter-grain exchange coupling in the Nd2Fe14B/alpha-Fe-type nanocomposites. For as-annealed Nd8.4Fe87.1-xMoxB4.5 (x=0, 0.6, 1.1 and 1.6) and Nd8.4Fe80.4Co5.6Mo1.1B4.5 alloys, the intrinsic coercivity mu(0)H(c) and the maximum magnetic energy product (BH)(max) are remarkably improved in the alloys with only Mo-additions as well as in the Nd8.4Fe80.4Co5.6Mo1.1B4.5 alloy. The improvement of the magnetic properties is the result of an enhancement of the exchange coupling, because of the modifications of nanostructural factors and phase components by a proper substitution of 3d elements for Fe. (C) 2002 Elsevier Science B V All rights reserved.