Study on narocrystalline Fe-based alloys with high saturation magnetization

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We carried out the fundamental study on the development of Fe-based soft magnetic materials with high saturation megnetization (Bs) above 1.6 T.As a result, the nanoscale bcc phase alloys obtained by partial crystallization of an amorphous phase in Fe-Co-Zr-Nb-B system were found to exhibit high Bs above 1.6 T,extremely high permeability (mue) of 10^5 at 1kHz and nearly zero magnetostriction (lambdas). The most appropriate composition was determined to be Fe-2at%Co-2%Zr-5%Nb-5%B.The use of this component enabled the production of long and wide amorphous sheets with 12 mm in width, 20 mum in thickness and more than 100 m in length by the single-roller quenching technique. This amorphous sheet had good bend ductility and ring-shape samples with 10 mm in diameter were prepared by mechanical punching. The annealing of the ring-shape samples for 3.6 ks at 873 K caused the formation of the nanocrystalline structure consisting of bcc particles with a diameter of 10 to 20 nm surrounded by the … More amorphous phase with a thickness of about 5 nm. The nanobeam compositional analyzes indicate that the Co element is enriched in the bcc particles while the Zr, Nb and B elements are segregated to the amorphous phase. The redistribution of the constituent elements was essential for the formation of the nanocrystalline structure leading to the appearance of the good soft magnetic properties combined with high Bs. We also pointed out that the particle size and interparticle spacing of the bcc particles were smaller than the width of magnetic domain wall and the nanoscale mixed structure enabled the achievement of the exchange interaction for the appearance of ferromagnetism. Subsequently, the nanocrystalline ring-shape sheets were laminated with epoxy resin for the purpose of application, and the core losses and mue as a function of frequency in a range of 50 Hz to 10 MHz were measured for the laminated sheets. As a result, the laminated sheets were found to exhibit much better soft magnetic properties as compared with those for conventional Fe-3 mass%Si steel and Fe-Si-B amorphous sheets because of the simultaneous satisfaction of high Bs and zero lambdas. Consequently, the present nanoscale bcc alloys are expected to be used as a new type of soft magnetic material with high Bs. Less