The origin of high magnetic properties in (R,Zr)(Fe,Co)11.0-11.5Ti1.0-0.5Ny (y=1.0-1.4 for R=Nd, y=0 for R=Sm) compounds

Ten alloys and nitrogenated compounds of (R,Zr)(Fe,Co)11.0-11.5Ti1.0-0.5Ny (y=1.0-1.4 for R=Nd, y=0 for R=Sm) with a ThMn12-type structure were prepared. The average Fe-Fe interatomic distances, d(Fe-Fe), for Fe sites were calculated based on the reported atomic parameters. The hyperfine splittings (inner field (IF), in teslas) were measured by Mössbauer spectroscopy, and the IF increased with increasing d(Fe-Fe) for Fe sites, indicating a magneto-volume effect. The order of IF magnitude in Fe sites was Fe(8i)>Fe(8j)>Fe(8f) in all alloys. Co substitution for Fe sites, (Fe0.75Co0.25), increased the IF by 25% for the R=Nd alloy and 15% for the R=Sm alloy. Decreasing Ti content from −Ti1.0 to −Ti0.5, which increased the Fe and Co content, preserved the ThMn12 structure with Zr substitution for R(2a) sites, and caused a slight increase in the IF of 2% for the R=Nd alloy and 7% for the R=Sm alloy. Nitrogenation, where N was introduced into the 2b sites, also increased IF in R=Nd alloys, by 23% for the Co- and Zr-free alloys, NdFe11Ti1.0N1.5, and by 7% for the Co-containing, (Nd0.7Zr0.3) (Fe0.75Co0.25) 11.5Ti0.5N1.3 alloy. The IF values of the R=Nd alloys were slightly larger than those of the R=Sm alloys. In conclusion, the magneto-volume effect was clearly observed at the Fe sites, and Co substitution into Fe sites and nitrogenation (R=Nd alloys) compensated for the increased IF. Increasing the Fe and Co fractions also increased IF slightly.