STRUCTURE AND MAGNETIC-PROPERTIES OF R2CO17-XSIX (X = 0-3) COMPOUNDS WITH R = Y AND PR

The influence of Si substitution for Co or, the structure and magnetic properties of Y2Co17-xSix and Pr2Co17-xSix (x = 0-3) compounds were i nvestigated by means of x-ray diffraction and magnetization measuremen ts. X-ray diffraction patterns demonstrate that all samples are single phase with the hexagonal Th2Ni17-type structure for Y2Co17-xSix and t he rhombohedral Th2Zn17-type structure for Pr2Co17-xSix compounds, exc ept for Pr2Co14Si3 With a small amount of impurity phases. The unit-ce ll volume is found to decrease linearly with increasing Si concentrati on in both series. The Curie temperature decreases monotonically with increasing Si concentration at an approximate rate of 205 and 175 K pe r Si atom for the Y2Co17-xSix and Pr2Co17-xSix compounds, respectively . The saturation magnetic moments of R2Co17-xSix (R = Y, Pr) decrease with increasing Si content and the decline rates are larger than that expected as a simple dilution. For Y2Co17-xSix, the substitution of Si has a significant effect on the magnetocrystalline anisotropy of the Co sublattice, and changes the easy magnetization direction from the b asal plane to the c-axis at room temperature. For Pr2Co17-xSix, the Si substitution has not changed the easy magnetization direction at room temperature. However, the spin-reorientation transitions from the bas al plane to the c-axis for this series with 0.5 less than or equal to x less than or equal to 2.4 were observed above room temperature with increasing temperature. The spin-reorientation temperature TSR first d ecreases with increasing Si content and then increases at higher x val ues (x > 2). The origin of this spin reorientation is interpreted by t he competition between the Pr sublattice anisotropy and the Co sublatt ice anisotropy. This has been confirmed by the magnetocrystalline anis otropy measurements on Y2Co17-xSix.