Structural and magnetic properties of PrFe10Mo2Ny prepared by hydrogenation-disproportionation-desorption-recombination and nitrogenation processes

Hydrogenation-disproportionation-desorption-recombination (HDDR) process has been used as a pretreatment to prepare isotropic Pr(Fe,Mo)(12)N-y compounds. The phase component, microstructure and magnetic properties of the nitrided powders have been investigated systematically Pr(Fe,Mo)(12) absorbs interstitial hydrogen on heating at 200-350 degrees C and forms isostructural Pr(Fe,Mo)(12)H-x hydrides accompanied with a slight lattice expansion corresponding to 0.9% of the cell volume. The disproportionation reaction of hydrogen with Pr(Fe,Mo)(12) above 580 degrees C results in the occurrences of PrHdelta, Fe2Mo and alpha-Fe. As the samples hydrogenated at 750 degrees C are degassed at 650 degrees C in a vacuum, a metastable phase with TbCu7-type crystal structure forms. With increasing dehydrogenation temperature to 750 degrees C, the TbCu7-type phase transforms into Pr(Fe,Mo)(12) compounds. Above 850 degrees C, Pr(Fe,Mo)(12) partially decomposes and the amount of alpha-Fe increases. The optimum temperature for the HDDR process is 750 degrees C for preparing the isotropic Pr(Fe,Mo)(12)N-y, magnets. Upon nitrogenation at 425 degrees C, the Curie temperatures of 1 : 7 and 1 : 12 type nitrides are found to be about 395 and 303 degrees C, respectively, and a best coercivity of 3.4 kOe with a magnetization up to 122 emu/g at a field of 2 T is obtained for 1 : 12 compounds without fine milling. The coercivity is probably arised by the reverse domain nucleation mechanism. (C) 1998 Elsevier Science B.V. All rights reserved.