Spin fluctuations and Curie temperature in the compounds R2M17 with nonmagnetic elements

The magnetic properties of materials for permanent magnets based on binary compounds R₂M₁₇ (R=Y, Sm; M=Fe, Co), also including additions of the nonmagnetic elements N, Al, and Si, are investigated a the theory of dynamical fluctuations of the electronic spin density. It is shown that the Curie temperature is determined by the ratio of the exchange splitting energy (proportional to the magnetization at T=0) and the rms value of the fluctuations (proportional to the local spin susceptibility). The fluctuations are much larger in iron compounds than in cobalt alloys. This results not only in quantitative differences in their characteristics but also in a qualitatively different change in the properties of these materials on nitriding. Fiz. Tverd. Tela (St. Petersburg) 41, 77–83 (January 1999)