Magnetic Behavior of Sintered NdFeB Magnets on a Long-Term Timescale

Abstract EN

Stable polarization of permanent magnets over the lifetime of the application is an important aspect in electrical machine design.

Specification of the long-term stability of magnet material is difficult, since knowledge of the phenomenon is incomplete.

To be able to optimize magnet material selection, the long-term magnetic behavior of the material must also be understood.

This study shows that material with a very square JH curve is stable until a certain critical operating temperature is reached.

Major losses are detected as the critical temperature is exceeded.

Material with a rounder JH curve does not show a well-defined critical temperature, but increasing losses over a large temperature range.

The critical temperature of a material is also dependent on the field conditions.

Results differ whether the tests are performed in an open or closed magnetic circuit.

In open-circuit tests, the opposing field is not homogeneously distributed throughout the volume of the magnet and thus the long-term behavior is different than that in closed-circuit conditions.

Open-circuit tests seem to give bigger losses than closed-circuit tests in cases where the permeance coefficient of the open-circuit sample is considered to be the average permeance coefficient, calculated according to the dimensions of the magnet.