Unusual Strain Resulted from Interaction Between Permanent Magnets

Abstract

Detailed investigations of the properties essential for the interaction of permanent NdFeB magnets were performed at T=300 and 77 K. Axial and radial magnetic field distribution, attracting force, and work are well described using a single-turn substitutional coil model. Strain resulting from the interaction of magnets was calculated and measured for the first time. Unexpected radial strain and additional negative change in the magnet volume were revealed in the experiment performed at T=77 K. This additional change in the volume was proportional to the diminishing of the magnet free energy. A similar dependence was observed for the magnetostriction. It was concluded that any change in the magnetic free energy F_m is accompanied by the change in the elastic free energy ΔF_e ≈ 0.1ΔF_m at T=77 K. At room temperature, ΔF_e is much smaller than ΔF_m.