Structural, microstructural and magnetic properties of nanocomposite isotropic Sm(CobalFe0.1MyZr0.04B0.04)7.5 ribbons with M=Ni, Cu and y=0.09 and 0.12

In boron-substituted melt-spun Sm(Co,Fe,Cu,Zr)7.5-type alloys a nanocomposite microstructure and high coercivities in both as-spun and short-time annealed ribbons can be obtained. In the present study three different compositions, namely Sm(Co0.73Fe0.1Cu0.09Zr0.04B0.04)7.5, Sm(Co0.70Fe0.1Cu0.12Zr0.04B0.04)7.5 and Sm(Co0.70Fe0.1Ni0.12Zr0.04B0.04)7.5 have been examined in order to investigate the influence of composition on the magnetic properties and the microstructure. Melt-spun ribbons have been obtained and annealing has been followed under argon atmosphere for 30-75 min at 600-870 °C. For the as-spun ribbons the TbCu7-type of structure and fcc-Co as a secondary phase have been identified in the X-ray diffraction patterns. For the annealed ribbons above 700 °C the 1:7 phase transforms into 2:17 and 1:5 phases. The TEM studies have shown a homogeneous nanocrystalline microstructure with average grain size of 30-80 nm. Coercivity values of 15-27 kOe have been obtained from hysteresis loops traced in non-saturating fields. The coercivity decreases with temperature, but it is sufficiently large to maintain values higher than 5 kOe at 380 °C.