High-temperature and frequency-dependent properties and structural evolution of HITPERM, an iron-cobalt-base nanocomposite soft ferromagnetic material

HITPERM is an FeCo-base nanocomposite soft ferromagnetic alloy. Its nominal composition is (Fe_xCo_1−x) ₈₉M₇B₄ (M = Zr, Nb, Hf) and its structure is composed of nanocrystalline B2 ordered FeCo grains embedded within an amorphous matrix. Its soft magnetic properties are an emergent phenomenon of its nanocrystalline grain size, as predicted by the Random Anisotropy Model, which is reviewed. HITPERM is distinguished from other nanocomposite alloys by its high amorphous phase Curie temperature. This allows nanocrystalline grains to remain exchange coupled to 600°C, which is demonstrated. The Curie temperature of the amorphous phase is shown to be reduced by the addition of Cr. The core loss of HITPERM is measured and found to be comparable to a commercially available Fe₄₉Co₄₉V₂ alloy. Core loss is reduced by compositional modification as well as by field annealing. The evolution of the structure of HITPERM is observed in the as-cast and partially crystallized ribbons. Zr is observed to be depleted near the surface of the as-cast ribbons and is suggested to be the cause of a crystalline layer in this region. Partially crystallized ribbons display a uniform grain size distribution on both sides of the ribbon. Cu is determined not to be an effective nucleation agent during crystallization. Zero-field reannealing of the field annealed and field crystallized samples suggests that a structural cause other than crystalline texture contributes to induced anisotropy.