Dependence of structures and performances of soft-magnetic FeCo-based metal glasses on cryogenic treatments

The amorphous structures, thermal stability, soft-magnetic properties and microhardness have been explored for quaternary quenched (Fe 0.8 Co 0.2 ) 75 B 21 Ta 4 (Fe0.8) and (Fe 0.5 Co 0.5 ) 75 B 21 Ta 4 (Fe0.5) metallic glasses (MGs) after deep (77 K), moderate (173 K) and shallow (253 K) cryogenic treatments (CTs). Compared to Fe0.5, the as-spun Fe0.8 exhibits significantly higher thermal stability and Curie temperature (686 K), which could be explained by the Mössbauer spectra results of higher A 23 and lower hyperfine magnetic field and isomer shift. But the as-spun Fe0.5 shows a more prominent magnetic rejuvenation trend. Additionally, the observation of Kerr microscope displays that magnetic domains around surface defects exhibit a trend from being easy to magnetize to becoming difficult with increasing reverse magnetic field intensity. The cryo-treated Fe0.8 and Fe0.5 ribbons maintaining a completely amorphous structure reveal the improved soft-magnetic property and microhardness, and the performance optimization of Fe0.5 is more sensitive to CTs. Appropriate CTs distinctly decrease coercivity ( H c ) of two tested MGs, and moderate CT reduces the H c of Fe0.5 by 24.1%, achieving commendable magnetic softening. The H c variation can be rationalized by the evolution of free volume in the amorphous matrix involving freezing, partial annihilation and imbalance under different CTs. Moreover, shallow CT significantly expands the heat-treatment processing window of MGs.