Amorphous-FeCoCrZrB ferromagnets for use as high-temperature magnetic refrigerants

Magnetic metallic glasses, having large magnetic moments and high Curie temperatures (T-C), have not been widely studied as magnetic refrigerants. In this study, we report on the magnetocaloric effects of five FeCoCrZrB amorphous alloys [(FexCoyCrz)(91)Zr7B2, with Fe:Co:Cr ratios of 100:0:0, 90:15:5, 85:5:10, and 75:15:10] chosen for efficiently surveying the high T-C metallic glass composition surface. Magnetic isotherms were measured at 25 K intervals from 25 to 525 K. The entropy change (Delta S) due to the magnetocaloric effect was computed by integrating the magnetic isotherms. The refrigeration capacity (RC) was computed by Wood-Potter method. At 3979 kA/m (50 kOe) the FeCoCrZrB alloys have RC values of 240-320 J/kg; at 796 kA/m (10 kOe) the alloys have values of 32-54 J/kg. The RC values favorably compare with values reported for other refrigerant materials. The peak Delta S temperature depends strongly on composition, varying from 200 to 450 K. The wide flexibility in choosing amorphous alloy compositions allows them to be fine tuned for multistage high temperature refrigerators. The saturation magnetization at 25 and 300 K and Curie temperatures are also reported for the five alloys. (C) 2006 American Institute of Physics.