Structure and magnetic properties of nanocrystalline Sm(Fe1-xCox)11Ti (x<=2)
Abstract
Magnetic properties correlated to structural transformations, from metastable hexagonal CaCu5-type phases to equilibrium tetragonal 1:12 phases, are studied systematically for nanocrystalline Sm(Fe1-xCox)11Ti alloys (x<=2). The Rietveld analysis gives a stoichiometry ratio equal to 1:10, for the out of equilibrium hexagonal precursor, which is described with three crystallographic transition-metal T sites: 3g is fully occupied, and 6l occupation is limited to hexagons surrounding the T dumbbell pairs 2e. The substitution of Co, in both structures, contributes to reduce the negative exchange interactions and results in Curie temperature enhancement. The hyperfine parameter assignment, on the basis of the Wigner-Seitz volume calculation, in the tetragonal structure points towards the Co 8f preferential occupation. The mean hyperfine field increase, with Co content, in the two phases, might be correlated to the compensation of the core-electron polarization field by the 4s polarization field produced by the 3d moment. The coercitive field of 0.6 T measured at room temperature suggests that nanocrystalline SmFe9Co2Ti, with a Curie temperature equal to 790 K, is a semihard material and is a potential candidate for magnetic recording.
- Publication:
-
Physical Review B
- Pub Date:
- February 2001
- DOI:
- 10.1103/PhysRevB.63.054412
- Bibcode:
- 2001PhRvB..63e4412B
- Keywords:
-
- 75.50.Bb;
- 75.50.Tt;
- 76.80.+y;
- Fe and its alloys;
- Fine-particle systems;
- nanocrystalline materials;
- Mossbauer effect;
- other gamma-ray spectroscopy