Rare earth-free hard magnetic microwires

Abstract

Novel microwires of composition MnBi were obtained by means of quenching and drawing technique having a metallic nucleus of 50 μm diameter. Phase distribution analysis showed a composite microstructure comprising extensive zones of the ferromagnetic hexagonal MnBi phase (of up to 12 μm), interspersed within a matrix of diamagnetic Bi and some inclusions of pure Mn varying between 1 and 2 μm in length. A coercive field in excess of 4000 Oe was measured. Coercivity mechanism is described in terms of nucleation of reverse domains, for which the interface MnBi/Bi largely determines the hard magnetic response of the composite microwire.