Impact of particles surface smoothing on DC permeability of NiFeMo soft magnetic powder compacts

Abstract Soft magnetic compacted powders exhibit excellent magnetic properties as low core losses, high permeability and 3-D isotropic magnetic behaviour, but they are also characterised by porous structure. In those materials, the inner demagnetizing fields arise primarily from ferromagnetic particles surfaces and negatively affect magnetic permeability. In presented work four Ni80Fe15Mo5 (supermalloy) compacted powder samples were studied. Two of the samples, differing in heat treatment, were compacted from powder particles obtained by mechanical milling (with irregular shapes) as the references, and for two others, the particles with mechanically smoothed surfaces (with spherical-like shapes and the morphological inhomogeneities removed) were used. DC magnetic permeabilities of the samples were investigated by the approach, which excludes the presence of porous structure and the inner demagnetizing fields. It allows to evaluate the exact impact of particles surface smoothing on the character of magnetization processes. It was found that particle surface smoothing improved the movability of domain walls, therethrough the increase of magnetic interaction between individual particles. After the heat treatment, it leads to enormous rise of differential, reversible and irreversible permeabilities of NiFeMo compacts at the lower levels of magnetic fields.