Structural and magnetic properties of PrFe12-xVx and their nitrides

The structural and magnetic properties of novel permanent magnet materials, PrFe12-xVxNy (x = 1.25 similar to2.0; y approximate to1.6), have been studied systematically. It is shown that the nitrides crystallize in the same ThMn12-type structure as the parent alloys, with the unit cell volume expansion upon nitrogenation. Neutron diffraction performed on PrFe10.5V1.5N0.4 at room temperature reveals that the vanadium atoms occupy the Si sites, while the nitrogen atoms occupy the 2b sites and the iron atoms occupy the 8j, 8f and the rest 8i sites in the ThMn12-type structure. Typical interstitial modification effects are observed in PrFe12-xVxN1.6. The Curie temperature is raised to as high as 800 K and the saturation magnetization is increased to 1.54 T at room temperature. Mossbauer spectra studies also show that the hyperfine field and isomer shift are strongly enhanced upon nitrogenation. Nitrogenation changes the easy magnetization direction from the ab-plane to the c-axis with an anisotropy field up to 10.5 MA/m (132 kOe). Crystal field coefficients For Pr3+ in PrFe12-xVx and PrFe12-xVxN are calculated to explain this change in magnetocrystalline anisotropy behaviors. As a preliminary attempt, the magnetically hard powders based on Pr(Fe,V)(12)N-1.6 are obtained with a maximum energy product of 135 kJ/m(3) (16.9 MGOe) and a remanence of 1.18 T at room temperature. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.