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 propert ies of the intermetallic La2Co17-xMox (x = 0.5, 1, 1.5, 2), and La2Co16-yFe yMo (y = 0, 1, 2, 3, 4, 6) compounds have been studied by X-ray diffractome try, magnetic measurements and Mossbauer spectroscopy. All samples belong t o the rhombohedral Th2Zn17-type structure and their lattice parameters a an d c increase both with Mo and Fe content. From the La-Co-Mo samples only th e one with x = 0.5 presents planar anisotropy, whereas from the La-Co-Fe-Mo samples only the y = I has uniaxial anisotropy. The magnetization Ms and t he Curie temperature T-C decrease upon Mo substitution, whereas the anisotr opy field H-A does not change significantly. In the Fe-substituted compound s M-S increases, but the Curie temperature increases slightly for 0 less th an or equal toy less than or equal to4 but decreases in y = 6. The low temp erature M-T curve shows that the samples La2Co16.5Mo0.5, and La2Co10Fe6Mo p resent a spin reorientation transitions at 70 and 260K, respectively. Mossb auer 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 a nd quadrupole splitting parameters is observed which can be associated to t he spin reorientation. (C) 2001 Elsevier Science B.V. All rights reserved.