Structure and magnetic properties of Gd2Co17-xSix compounds

The Gd2Co17-xSix compounds have the rhombohedral Th2Zn17 structure and form for 0 less than or equal to x less than or equal to 3. The compounds with 0 less than or equal to x less than or equal to 0.3 have an easy magnetisation direction parallel to the c axis only at high temperatures. The spin reorientation temperature, leading to a state with easy magnetisation direction perpendicular to the c axis, decreases strongly with increasing Si concentration. The spin reorientation in Gd2Co17 takes place at 940 K, which is substantially lower than that reported previously for Ho2Co17. The componds with 1 less than or equal to x less than or equal to 3 have an easy magnetisation direction parallel to the c axis at all temperatures. The Co moments and the Curie temperatures decrease strongly with increasing Si concentration. We also determined the values of the anisotropy constant K-1 which change from negative to positive around x = 0.7. This behaviour is discussed in terms of preferential Si substitution. (C) 1999 Elsevier Science B.V. All rights reserved.