Magnetism and phase structure of crystallized Sm–Fe–B melt spun ribbons

The crystallization of amorphous Sm_xFe_80−xB₂₀ melt spun ribbons is studied over an extended range of composition (0 < x < 8). Differential scanning calorimetry scans reveal different endo- and exothermic effects depending upon the composition. X-ray diffraction and Mössbauer studies for samples annealed at temperatures close to the onset of the first exothermic effect prove that, during the primary crystallization of the amorphous ribbons, both α-Fe and Fe₃B phases appear—with Sm ions randomly accommodating the Fe sites in the tetragonal Fe₃B lattice—while the subsequent exothermic reactions correspond to the decomposition of the metastable Fe₃B phase into α-Fe and Fe₂B and to the formation of the ternary Sm_1.1Fe₄B₄ phase. Fully crystallized ribbons with Sm contents lower than about 7 at.% show the co-existence between α-Fe and Fe₂B soft magnetic phases and the Sm₂Fe₁₄B magnetic one. The enhancement of magnetic properties with increasing relative proportion of magnetic phase is discussed and correlated with exchange coupling and spin wave stiffness data obtained from the magnetic measurements.