Rare-earth moment reduction and local magnetic anisotropy in Pr2Fe14B and Tm2Fe14B

Abstract Magnetization curves for Pr2Fe14B single crystals were measured between 300 K and 900 K. The saturation magnetization Ms along the [1 0 0] direction was found to be 3% to 6% smaller than that for the [0 0 1] direction, not only at 300 K but also up to the Curie temperature. Published magnetization curves for Tm2Fe14B single crystals were reexamined, in which Ms along the [0 0 1] direction exceeds that for the [1 0 0] direction. We attributed these differences in Ms to the reduction of the rare-earth (R) moment when forced to be aligned along the hard direction by external fields. Significant anisotropy was observed in the paramagnetic susceptibility χ up to 900 K in the Pr2Fe14B (R = Pr) system. Based on the crystalline electric field parameters for R = Pr and Tm systems obtained by first-principles calculations, we numerically evaluated the magnetization and paramagnetic susceptibility at high temperatures. The differences in Ms and χ obtained from the calculation were in good agreement with the experiments. We found that the reduction rate for the Pr moment at the 4f site is much smaller than that at the 4 g site. This result suggests a crucial decrease in the local magnetic anisotropy at the Pr(4f) site.