Soft Magnetic Properties of Nanostructured Vitroperm Alloy Powder Cores

Magnetic properties of amorphous and nanocrystalline samples have been experimentally investigated. Rapidly quenched ribbons of Fe₇₃Cu₁Nb₃Si₁₆B₇ (Vitroperm 800) were ball-milled and cryomilled to powder and warm-consolidated (at a pressure of 700 MPa) to get bulk compacts. It was found by investigating the influence of mechanical milling on the magnetic properties of powder samples prepared by milling that the alloy remains amorphous during the whole milling process. The frequency dependence of the coercivity and total core losses were studied. Investigation of the dc coercivity, magnetostriction, and electrical resistivity were done. Annealing at higher temperature causes a deterioration of dc soft magnetic properties. The higher coercivity of the as-prepared samples is mainly due to interfaces of the powder elements and internal stresses created by milling and consolidation that were decreased greatly after annealing. The frequency dependence of magnetic properties is also illustrated, and it is attributed mainly to the domain wall damping. The absolute values of losses and coercivity of Fe-based compacts are similar to that for Co-based compacts. We have prepared bulk samples in the form of the small cylinders with coercivity down to 13 A/m. These materials have more degrees of freedom for tailoring their magnetic properties due to their flexibility in shape and dimensions.