Deep supercooling solidification towards tuned amorphous/nanocrystalline dual phases for superior magnetic nanocrystalline alloys

Nanocrystalline soft magnetic alloys featuring with amorphous-nanocrystalline dual-phase structure are critical for energy conversion and transportation at elevated frequencies. Their applications however, are refrained by limited saturation magnetic flux density (B_s) due to unavoidable addition of a considerable quantity of non-magnetic elements for glass forming ability (GFA). Furthermore, engineering of the amorphous-nanocrystalline microstructure is critical for the coercivity (H_c), which urges development of advanced approach. In this study, a deep supercooling solidification has been proposed, which not only promotes the formation of short-range packing and icosahedron/icosahedron-like structures for enhanced GFA, but also induces an optimized microstructure consisting of highly disordered amorphous matrix to facilitate nanograin refinement. Based on such strategy, Finemet-based nanocrystalline alloy with superior magnetic properties (B_s = 1.71 T, H_c = 5.0 A/m) has been achieved without additional glass forming element. Such superior performance is correlated to the unique magnetic domain structure involving straight domain walls and smooth movement. The deep supercooling strategy not only breaks the trade-off between the B_s and GFA to allow the design of nanocrystalline alloys with large ferromagnetic content, but also serves as an effective method for microstructure optimization for nanocrystalline alloys.