Modeling of magnetic properties of heat treated Dy-doped NdFeB particles bonded in isotropic and anisotropic arrangements

The effects of compacting methods, heat treatment and chemical additives on the magnetic properties of NdFeB particles have been studied. Five sets of NdFeB powder particles, doped with different amounts of Dy from 0.1-2.9 wt%, were prepared in powder form by gas atomization and annealed at 650-750 degrees C for 600 seconds under an inert argon atmosphere. These were then bonded in epoxy, either in isotropic form, or aligned during fabrication under the action an applied magnetic field. Their magnetic properties were measured using a vibrating sample magnetometer. The results showed that the combined effects of the addition of Dy and heat treatment could dramatically improve the coercive force, remanent magnetization and maximum energy product. The results have been interpreted using a model of hysteresis which takes into account energy losses, anisotropy and texture of a material. The modeling showed that these effects alter the magnetic properties by increasing the hysteresis loss via the loss coefficient and by reducing the reversible component of magnetization through the reversibility coefficient; The compacting process influences the density of the particles in the bonded magnet which alters the magnetic properties through the coupling coefficient. The major influence of particle alignment can be interpreted as a change in the texture which can be described by a texture parameter.