Structure and magnetic properties of ( x = 0-3) compounds with R = Y and Pr

The influence of Si substitution for Co on the structure and magnetic properties of and (x = 0-3) compounds were investigated by means of x-ray diffraction and magnetization measurements. X-ray diffraction patterns demonstrate that all samples are single phase with the hexagonal -type structure for and the rhombohedral -type structure for compounds, except for with a small amount of impurity phases. The unit-cell volume is found to decrease linearly with increasing Si concentration in both series. The Curie temperature decreases monotonically with increasing Si concentration at an approximate rate of 205 and 175 K per Si atom for the and compounds, respectively. The saturation magnetic moments of (R = Y, Pr) decrease with increasing Si content and the decline rates are larger than that expected as a simple dilution. For , the substitution of Si has a significant effect on the magnetocrystalline anisotropy of the Co sublattice, and changes the easy magnetization direction from the basal plane to the c-axis at room temperature. For , the Si substitution has not changed the easy magnetization direction at room temperature. However, the spin-reorientation transitions from the basal plane to the c-axis for this series with were observed above room temperature with increasing temperature. The spin-reorientation temperature first decreases with increasing Si content and then increases at higher x values (x > 2). The origin of this spin reorientation is interpreted by the competition between the Pr sublattice anisotropy and the Co sublattice anisotropy. This has been confirmed by the magnetocrystalline anisotropy measurements on .