Magnetic properties of Sm(CobalFe0.31Zr0.05Cu0.04Bx)z alloys and their melt-spun materials (x=0.02--0.04,z=7.5--12)

Cast alloys and melt-spun ribbons with nominal compositions of Sm(Co_balFe_0.31Zr_0.05Cu_0.04B_x)_z (x=0.02-0.04,z=7.5-12) have been synthesized and characterized in a temperature range of 10-1273 K and at fields up to 5T. The main phase in the as-cast alloys exhibited a Th₂Ni₁₇ type structure, with a strong uniaxial anisotropy. Minor phases with a TbCu₇ and/or CaCu₅ structure emerged as z (3d/R) decreased. As a result, the anisotropy field (H_A) increased from 67 to 120 kOe, while 4πM_s fell from 12.8 to 10.5 kG at 300 K when z was decreased from 12 to 7.5. For melt-spun ribbons, they are nano-structured in nature and magnetically hard, even in the as-spun state. By lowering the value of z(3d/R) and raising the B content, a finer microstructure and a higher H_ci were obtained. Hard magnetic properties of H_ci=4.9-12 kOe, 4πM_s=9.0-12.0 kG at 300 K have been obtained from ribbon samples. Among them, Sm(Co_balFe_0.31Zr_0.05Cu_0.04B_0.02)₁₀ ribbon showed the highest (BH)_max of 10.8 MGOe at 300 K. A Henkel plot analysis suggested the existence of exchange-coupling interaction between the magnetically hard and soft phases in the ribbon materials.