Structure and magnetic properties of the intermetallic La2Co17−xMox (x=0.5, 1, 1.5, 2) and La2Co16−yFeyMo (y=0, 1, 2, 3, 4, 6) compounds

The effect of Mo and Fe atoms on the crystal structure and magnetic properties of the intermetallic La2Co17−xMox (x=0.5, 1, 1.5, 2), and La2Co16−yFeyMo (y=0, 1, 2, 3, 4, 6) compounds have been studied by X-ray diffractometry, magnetic measurements and Mössbauer spectroscopy. All samples belong to the rhombohedral Th2Zn17-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 MS and the Curie temperature TC decrease upon Mo substitution, whereas the anisotropy field HA does not change significantly. In the Fe-substituted compounds MS 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 La2Co16.5Mo0.5, and La2Co10Fe6Mo present a spin reorientation transitions at 70 and 260K, respectively. Mössbauer samples were obtained for all Fe-containing samples in the temperature range 20–300K. Above 260K a jump in the values of the hyperfine fields and quadrupole splitting parameters is observed which can be associated to the spin reorientation.