Nanograined YCo5-based powders with high coercivity

Highly-coercive YCo5-based nanograined powders with composition YxCo100-x ( x = 16.8-20) have been synthesized by mechanical milling of as-cast alloys and subsequently annealing them. The optimum magnetic properties have been obtained in Y19.5Co80.5 powders milled for 4 h and annealed at 950 degrees C for 1 min with a coercivity of 16.0 kOe, a high M-t/M-s ratio of 0.67 and a medium-strength maximum energy product (BH)(max) of 7.7 MG Oe, Microstru cture studies reveal that the Y19.5Co80.5 powders have a nearly single YCo5 structure with a grain size of about 30-40 nm. The high coercivity is attr ibuted to the high anisotropy field of the YCo5 phase and to its nanoscale grain size. (C) 2000 Elsevier Science B.V. All rights reserved.