STRUCTURAL AND HARD MAGNETIC-PROPERTIES OF RAPIDLY SOLIDIFIED SM-FE-N

Sm-Fe alloys have been produced by rapid quenching and the resulting phases have been investigated in the as-quenched state and after nitriding. Besides the well-known equilibrium phases of the binary Sm-Fe system (Fe, Sm2Fe17, SmFe3, SmFe2 and Sm), a hexagonal TbCu7-type phase shows up in melt spun ribbons (a = 4.88 angstrom, c = 4.23 angstrom). Its stoichiometry is about Sm1Fe9 and it is formed only at wheel velocities above 15 m/s. The Curie temperature and the saturation polarization of this new phase is 210-degrees-C and 1.25 T, respectively. At higher Sm concentrations or lower quenching rates the structure changes to the Th2Zn17-type. The Th2Zn17-type ribbons are magnetically soft whereas the TbCu7-type samples show moderate coercivities of up to 1.7 kA/cm. Nitrogenation leads to an expansion of the lattice and to an overall improvement of the hard magnetic properties for both phases. Their Curie temperatures are increased to 470-degrees-C and the saturation polarizations are raised to 1.40 and 1.51 T for the TbCu7- and the Th2Zn17-type phases, respectively. The best hard magnetic properties for isotropic TbCu7-type material are obtained for quenched, annealed and nitrided Sm10.6Fe89.4 which shows a coercivity, H(ci), of 4.9 kA/cm, a remanence, J(r), of 0.86 T and an energy product, (BH)max, of 69.6 kJ/m3. For similarly treated Sm12Fe88, which crystallizes in the Th2Zn17 structure, a coercivity of 16.7 kA/cm, a remanence of 0.73 T and an energy product of 65.6 kJ/m3 are achieved.