Syntheses and magnetic properties of Rm+nCo5m+3nB2n compounds

New compounds Pr3Co13B2 and Nd5Co19B6 have been synthesized successfully. They belong to the Rm+nCo5m+3nB2n 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) Angstrom and c = 10.6850(6) Angstrom, while Nd5Co19B6 is isostructural to Lu5Ni19B6 With a = 5.1328(3) Angstrom and c = 16.6519(5) Angstrom. Magnetic measurements indicate that Pr3Co13B2 is ferromagnetic with a Curie temperature of 360 K. Its saturation magnetic moment at 5 K is 20.0 mu(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 mu(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.