Magnetic properties and crystal structure of R₂Co_17-xGa_x compounds

We have studied the magnetic properties of several R₂Co_17−xGa_x compounds with R=Y, Tb, Dy and Ho. X-ray diffraction measurements made on magnetically aligned powders of Y₂Co_17−xGa_x compounds showed that these materials retain their easy-plane magnetisation at room temperature up to at least x=5. The difference in behaviour with the corresponding Gd compounds and the absence of spin-reorientation phenomena in R₂Co_17−xGa_x compounds in which the R component has a negative second-order Stevens factor is discussed in terms of preferred site occupation of the Ga atoms. High-field measurements at 5 K were made on free powders of several Tb, Dy and Ho compounds. The intrasublattice constants derived from these data are somewhat smaller than those of the undiluted R₂Co₁₇ compounds, which is also discussed in terms of preferred Ga site occupation.