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The effect of Mo and Fe atoms on the crystal structure and magnetic properties of the intermetallic La 2 Co 17− x Mo x ( x =0.5, 1, 1.5, 2), and La 2 Co 16− y Fe y Mo ( y =0, 1, 2, 3, 4, 6) compounds have been studied by X-ray diffractometry, magnetic measurements and Mossbauer spectroscopy. All samples belong to the rhombohedral Th 2 Zn 17 -type structure and their lattice parameters a and c increase both with Mo and Fe content. From the La–Co–Mo samples only the one with x =0.5 presents planar anisotropy, whereas from the La–Co–Fe–Mo samples only the y =1 has uniaxial anisotropy. The magnetization M S and the Curie temperature T C decrease upon Mo substitution, whereas the anisotropy field H A does not change significantly. In the Fe-substituted compounds M S increases, but the Curie temperature increases slightly for 0⩽ y ⩽4 but decreases in y =6. The low temperature M–T curve shows that the samples La 2 Co 16.5 Mo 0.5, and La 2 Co 10 Fe 6 Mo present a spin reorientation transitions at 70 and 260 K, respectively. Mossbauer samples were obtained for all Fe-containing samples in the temperature range 20–300 K. Above 260 K a jump in the values of the hyperfine fields and quadrupole splitting parameters is observed which can be associated to the spin reorientation. |
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