DIRECT DETERMINATION OF PRASEODYMIUM VALENCE IN PR2(COXFE1-X)14B

Using x-ray-absorption near-edge spectroscopy (XANES) the Pr valence in the pseudoternary Pr2(CoxFe1-x)14B compounds has been directly determined. Praseodymium L(III) edge XANES structures were obtained for the x=0, 0.3, 0.5, 0.7, and 1 compositions spanning the entire Co concentration range. It is found that the Pr valence is constant through the series and is identical to that in formally trivalent praseodymium acetate. The results demonstrate that the anomalous variation of the magnetocrystalline anisotropy with x in the Pr2(CoxFe1-x)14B compounds vis-a-vis their Nd-based counterparts does not arise from a Pr valence instability, as has been speculated in the literature, but must originate elsewhere. For comparison purposes XANES spectra for some relevant Ce and Nd materials are also reported.