EFFECTS OF SI SUBSTITUTION ON MAGNETIC-PROPERTIES OF GD2TM17 WITH TM = FE AND CO

The effect of substituting small amounts of Si for Fe and Co on the st ructure and magnetic properties of are-melted Gd2TM17 (TM = Fe and Co) compounds were studied by means of x-ray diffraction and magnetizatio n measurements. X-ray diffraction study of Gd2TM17-xSix indicates that the samples are single phase with the rhombohedral Th2Zn17-type struc ture. The substitution of Si for Fe or Co leads to an approximately li near decrease in the unit cell volume. The saturation moment at 1.5 K decreases linearly with increasing Si concentration, being an approxim ately linear rate of about 3.3 mu(B) per substituted Si for Gd2Fe17-Si -x, and about 4.1 mu B for Gd2Co17-xSix. The Curie temperature Te of G d2Fe17-xSix is found to increase with increasing x from 476 K for x = 0 to 572 K for x = 3; however, T-c of Gd2Co17-xSix shows a monotonic d ecrease from 1213 to 651 K as x Increases from 0 to 3. X-ray diffracti on measurements of magnetically aligned powders show that the Gd2Fe17- xSix compounds with x = 0-3 have an easy-plane type of magnetic anisot ropy. The easy magnetization direction of Gd2Co17-xSix compounds chang es from basal plane to c-axis with increasing Si concentration. The sa mples with x = 2 and 3 exhibit uniaxial anisotropy at room temperature .