The best solution for locally applied coercivity

Coming back to the fact that diffusion magnets are always inhomogeneous, a question arises as to how to turn this into an advantage. The magnetic circuit does not need a homogenous material. Applications need a magnet that has a sufficiently high local coercivity at each position inside the magnet. Excessive coercivity can be a disadvantage and can lead to locally reduced remanence. In addition, there is no physical reason why high-field concentrations should appear inside a magnet. The field density in electrical machines invariably has `hot spots` at the magnet surface. Since the diffusion process starts from the surface and gives a gradient to the magnet`s centre, the diffusion process is the best solution for locally applied coercivity.

The most recent development in reducing heavy rare earths in a sintered NdFeB magnet is local diffusion according to the local requirement of coercivity. JL MAG refers to this as three-dimensional grain-boundary diffusion (3D-GBD). Large reductions in heavy rare earth usage result in significantly associated price reductions, having been observed for several traction-machine projects.

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