Nanocrystalline softmagnetic materials
Nanocrystalline soft magnetic materials are composed of nanosized (~10 nm) grains of Fe and remaining amorphous phase. Due to the exchange coupling of randomly oriented grains of Fe, the magnetocrystalline anisotropy is averaged out to be zero. Magnetostriction can also be cancelled by a combination of positive values for the crystalline phase and negative values for the remaining amorphous phase, resulting in zero magnetostriction.
Fig. 1 Process, microstructure, coercivity dependence on grain size and applications of nanocrystalline soft magenetic materials.
Since magnetic softness can be achieved by the microstructure control rather than the intrinsic magnetic properties of alloys, there's much more freedom in alloy design. Fig. 2 shows permeability and saturation magnetic flux densities of representative nanocrystalline soft magnetic materials. Since the compositions of nonmagnetic elements can be reduced in the alloy design, higher saturation magnetic flux density can be obtained in the nanocrystalline soft magnetic materials compared to the existing bulk softmagnetic materials.
Fig. 2 Permeability and saturation magnetic flux densities of representative
alloys. Typical compositions, types of primary phases, saturation magnetic
flux density are tabulated.
The nanocrystalline soft magnetic material was commercialized by Hitachi Metalis with a trade name of FINEMET in Japan and by Vacuumschmelze with a trade name of Vitroperm in Europe.
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