Reduction of Nd moments and local magnetic anisotropy in Nd2Fe14B single crystals

Magnetization curves for Nd2Fe14B single crystals were measured between 300 K and 900 K. The saturation magnetization Ms along the [100] direction was found to be 2% to 4% smaller than that for the [001] direction, not only at 300 K but also up to the Curie temperature. We attributed this difference in Ms to the reduction of the Nd moment when forced to be aligned by external fields. Significant anisotropy was observed in the paramagnetic susceptibility χ up to 900 K. Based on the crystalline electric field parameters for Nd2Fe14B obtained by first-principles calculation, we calculated the magnetization and paramagnetic susceptibility χ. The difference in Ms and χ obtained from the calculation was in good agreement with the experiment. We found that the reduction rates for the Nd moments at 4f site are much smaller than that for the Nd moments at 4g site. This result therefore suggests a significant deterioration of local magnetic anisotropy at the Nd(4f) site even at elevated temperatures.