Syntheses and magnetic properties of R_m+nCo_5m+3nB_2n compounds

New compounds Pr₃Co₁₃B₂ and Nd₅Co₁₉B₆ have been synthesized successfully. They belong to the R_m+nCo_5m+3nB_2n family with m = 2, n = 1 and m = 2 and n = 3, respectively. Pr₃Co₁₃B₂ adopts the hexagonal La₃Ni₁₃B₂-type structure with lattice parameters a = 5.0672(3) Å and c = 10.6850(6) Å, while Nd₅Co₁₉B₆ is isostructural to Lu₅Ni₁₉B₆ with a = 5.1328(3) Å and c = 16.6519(5) Å. Magnetic measurements indicate that Pr₃Co₁₃B₂ is ferromagnetic with a Curie temperature of 360 K. Its saturation magnetic moment at 5 K is 20.0 µ_B fu^-1. Based on the results of the saturation magnetization, two kinds of Co sites with different magnetic moments are proposed. Pr₃Co₁₃B₂ exhibits large uniaxial anisotropy with an anisotropy field of 90 A m^-1 at 5 K. The Nd₅Co₁₉B₆ compound is ferromagnetic with a Curie temperature of 380 K. Its saturation magnetic moment and anisotropy field are 21.5 µ_B fu^-1 and 340 A m^-1 at 5 K, respectively. No spin reorientation was detected from the temperature dependence of the magnetization of these compounds from 5 K to their Curie temperatures, and the behaviour of magnetocrystalline anisotropy was analysed using the single-ion model.