Structural and magnetic properties of PrFe12−xVx and their nitrides

Abstract The structural and magnetic properties of novel permanent magnet materials, PrFe 12− x V x N y ( x =1.25∼2.0; y ≈1.6), have been studied systematically. It is shown that the nitrides crystallize in the same ThMn 12 -type structure as the parent alloys, with the unit cell volume expansion upon nitrogenation. Neutron diffraction performed on PrFe 10.5 V 1.5 N 0.4 at room temperature reveals that the vanadium atoms occupy the 8 i sites, while the nitrogen atoms occupy the 2 b sites and the iron atoms occupy the 8 j , 8 f and the rest 8 i sites in the ThMn 12 -type structure. Typical interstitial modification effects are observed in PrFe 12− x V x N 1.6 . 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 Pr 3+ in PrFe 12− x V x and PrFe 12− x V x N 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.