MAGNETOCRYSTALLINE ANISOTROPY OF Y2FE17-XGAX

A detailed study of the structural and magnetic properties of Y2Fe17-x Gax (x = 0-8) has been carried out to investigate the effects of Ga su bstitution on the Fe sublattice magnetic properties in general, and ma gnetocrystalline anisotropy, in particular. Powder X-ray diffraction r eveals a structural transition from the hexagonal Th2Ni17 structure fo r low Ga concentrations to a rhombohedral Th2Zn17 structure for high G a concentrations, with a critical Ga concentration of x(c) similar to 3. An expansion of the unit cell volume with Ga substitution, with a s lope of about 2.9 Angstrom(3)/f.u./Ga atom, is observed. This expansio n saturates x similar to 6. A simple model which can be used to extrac t the anisotropy constant from the magnetization data of magnetically aligned fixed powder samples (in the case of K-1 < 0) is proposed. The anisotropy field has a linear dependence on Ga substitution concentra tion, with a slope of similar to + 0.64 T/Ga atom. The planar anisotro py of Y2Fe17-xGax is weakened by Ga substitution and becomes uniaxial at Y2Fe11Ga6, The linear increase in the anisotropy field can be expla ined by the changes in the electronic structure after Ga substitution, The Curie temperature shows a maximum at x similar to 3-4, which is i n agreement with the literature value for substituted R(2)Fe(17-x)T(x) (T=Al, Ga, Si, Ti,...) compounds. The average Fe magnetic moment in Y 2Fe17-xGax varies from 2.06 mu(B), for x=0 to 1.83 mu(B) for x=4 at 10 K. The electronic structure plays a more important role than the atom ic size in determining the magnetic properties of the 2:17 phases.