Structural and magnetic properties of rhombohedral Sm2(Co,Fe,Cr)17Bx and Sm2(Co,Fe,Mn)17Bx compounds

Single-phase rhombohedral Sm₂(Co_balFe_0.2M_y)₁₇B_x with M = Cr or Mn substituting for Co have been prepared and the influence of transition metals on crystal structure, anisotropy field, and Curie temperature is examined. Sm₂Co₁₇ as-cast bulk sample has the 2 : 17 hexagonal structure (type Th₂Ni₁₇), while boron addition stabilizes the 2 : 17 rhombohedral structure (type Th₂Zn₁₇). Anisotropy field for Cr-doped as-cast sample is 74 kOe. Secondary phases of fcc-Co or Fe-Co are observed in some cases. A Cr-doped sample with y = 0.1 after annealing at 1190°C for 26 h is single phase. Curie temperatures of as-cast samples vary from ∼849°C to ∼687°C depending on the composition. Mechanical alloying and melt spinning were used to develop coercivity. As-spun ribbons at 53 m/s with Cr present a nanocomposite structure with H_c = 5.2 kOe. Samples with Mn have a coercive field close to 0.4 kOe. Scanning electron microscopy studies show different microstructure for Mn and Cr substituted ribbon samples.