MAGNETIC-PROPERTIES OF PR2CO17-XMX (M = GA, SI) COMPOUNDS

The influence of Ga or Si substitution for Co on the structural and ma gnetic properties of Pr2Co17 compounds is investigated. All samples st udied here are single phase and have the rhombohedral Th2Zn17-type str ucture. The unit-cell volume is found to increase linearly by the subs titution of Ga for Co, but reduce by the substitution of Si for Co in Pr2Co17 compounds. In Pr2Co17-xMx, the Curie temperature decreases mon otonically with increasing x at an approximate rate of 153K per Ga ato m and 175K per Si atom. The saturation magnetic moment of Pr2Co17-xMx( M = Ga, Si) decreases with increasing x. The rates of the decrease are larger than that expected as a simple dilution. For Pr2Co17-xSix,the spin-reorientation transition is observed above room temperature. The spin-reorientation temperature T-ST first decreases with increasing Si content and then increases at higher x values (x>2). The spin-reorien tation behavior is interpreted by the competition between the Pr and C o sublattice anisotropies. The easy magnetization direction in Pr2Co17 -xGax compounds is perpendicular to the c-axis, and no spin reorientat ion transition is observed.