Enhanced magnetocaloric effect of a partially crystalline Gd55Al20Ni25 bulk metallic glass

In this work, the magnetic properties and microstructure of a Gd55Al20Ni25 bulk metallic glass (BMG) heat-treated in the supercooled liquid region are studied. The as-cast rod annealed at the onset temperature of glass transition exhibits amorphous characteristics, and the magnetic properties similar to the as-cast rod. While the partially crystalline rod prepared by heating the as-cast rod to a temperature slightly lower than the onset of crystallization temperature and then rapidly cooling to room temperature shows enhancement of the peak value of the magnetic entropy change. The enhanced magnetocaloric effect of the partially crystalline rod was anomalous because the fully crystalline ingot exhibits much lower peak values of magnetic entropy change, indicating the possible formation of some metastable intermediate phases during nucleation and growth. The existence of some metastable phases was observed by careful microstructural investigations, and their formation mechanisms and magnetic properties were studied. (C) 2011 Elsevier Masson SAS. All rights reserved.