Nanocrystalline metastable 2/17 and 1/12 precursors: A promising class of hard magnetic materials.

We present a general structure model relative to the metastable P6/mmm precursors of the I4/mmm RFe11Ti (R=Pr,Sm) and R<OVERLINE>3</OVERLINE>m Sm2(Fe,M)17 (M=Ga,Si) equilibrium phases. This model is based on the description of the binary R1-sM5+2s compounds (s=vacancy rate, M=metal). The Rietveld analysis leads to stoichiometry consistency, respectively, with R(Fe,Ti,Co)10 and Sm(Fe,M)9. These results are corroborated by an accurate interpretation of the Mössbauer spectra. Intrinsic and extrinsic magnetic properties are presented. The precursors Sm(Fe,Ti,Co)10 and Sm(Fe,M)9C (M=Ga,Si) exhibit hard magnetic behavior. The compounds SmFe8.75M0.25C (M=Si,Ga) are particularly promising for permanent magnet applications. [ABSTRACT FROM AUTHOR]