Magnetic-domain structure of Nd₂Fe₁₄B permanent magnets

We report our studies of magnetic-domain structure in Nd₂Fe₁₄B permanent magnets using advanced transmission and scanning electron microscopy, including Lorentz imaging and electron holography. Domain-wall spacing D was measured as a function of thickness t for thin crystals, and also wall width of 90° and 180° domains; the domain-wall energies were calculated. Orientation and field dependence of the domain configuration and domain-wall behavior were examined in situ under different temperatures and applied fields. Characteristic magnetic structural features unique to corresponding bulk samples, such as reversed spike-domains and undulating domain boundaries, were also investigated.