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) 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 µB 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 µB 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.

Magnetic properties R(Fe1−xCox)11.3Nb0.7 compounds have been investigated. All of the compounds crystallize in the tetragonal ThMn12 structure. The unit cell volume slightly decreases with increasing Co content for both systems. Curie temperature (TC) almost increases linearly with increasing Co content for both systems. The maximum of saturation magnetization (Ms) appears around x=0.2 in Ho(Fe1−xCox)11.3Nb0.7 and x=0.15 in Y(Fe1−xCox)11.3Nb0.7 compounds at 5 K. The easy magnetization directions of all compounds are along the crystallographic c axis at room temperature. Thermomagnetic analysis shows that there exists no spin reorientation in the whole ordering temperature range. The magnetocrystalline anisotropy field Ba of Y(Fe1−xCox)11.3Nb0.7 exhibits a maximum with x=0.10 at 5 K and x=0.05 at room temperature, while Ba of Ho(Fe1−xCox)11.3Nb0.7 decreases monotonically with the increasing Co content at room temperature. First-order magnetization process (FOMP) has been observed in Ho(Fe1−xCox)11.3 compounds at low temperature.

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ErFe11-xGaxTi compounds with ThMn12-type structure were synthesized for x = 0, 1, 2, 3, 4, 5. The crystalline structure and Ga occupancy in the compounds were analysed in terms of the Rietveld method. With increasing Ga content, the lattice constant and unit-cell volume increase monotonically. Ti atoms are found to occupy 8i sites for all the compounds. Bond length and Ga occupancy factor are given. The Curie temperature increases first, going through a maximum and then decreases with increasing x while saturation magnetization decreases monotonically. Spin re-orientation from the uniaxial to the easy-cone type is detected for all the compounds as the temperature decreases from 300 to 5 K. A tentative spin phase diagram is constructed for the ErFe11-xGaxTi. In the ErFe11-xGaxTi compounds, a magneto-history effect is observed which can be attributed to irreversible movement of narrow domain walls that are easily pinned.