Structure and hysteresis properties of nanocrystalline FePt powders

Nanocrystalline hard magnetic Fe100-xPtx (x = 39.5, 45, 50, 55 and 60) powders have been prepared by mechanical ball milling at 77 K. With increasing x, the L1(0) volume fraction increases, reaching a maximum of about 85 vol% for Fe50Pt50. The FePt3 phase amount increases (LIP to 40 vol% in Fe40Pt60), whereas the Fe3Pt fraction reduces (from 38 vol% in Fe60.5Pt39.5) with increasing x. The coercivity was found to increase with x from 0.33 T (x = 39.5) to 0.95 T (x = 60), whereas the remanence reduces: from 0.8 T (x = 39.5) to 0.4 T (x = 60). Exchange-spring behaviour is observed for small values of x. (c) 2004 Elsevier B.V. All rights reserved.