Magnetoelastic anisotropy in NdFeB permanent magnets

The influence of magnetoelastic effects on the anisotropy in NdFeB permanen t magnets has been investigated. A relation between the magnetostriction co efficients and the magnetoelastic anisotropy is derived for crystals with t etragonal symmetry. Transmission electron microscopy experiments show that stress and strain are present at the boundaries of the Nd2Fe14B grains. The origin of the stress is discussed and an order-of-magnitude calculation of its effect on the anisotropy is provided for thermally induced stress. The calculations are in good agreement with the measured influence of stress o n coercivity. Both experiment and calculations show that homogeneous stress es have only a small influence on the coercivity. (C) 1999 American Institu te of Physics. [S0021-8979(99)04212-7].