MAGNETIC-PROPERTIES OF ERFEGA COMPOUNDS WITH THE 2 17-TYPE STRUCTURE/

An investigation of the structure and the magnetic anisotropy of Er2Fe 17-xGax compounds has been performed by means of X-ray diffraction and magnetization measurements. X-ray diffraction shows the prepared comp ounds to be single phase, having the hexagonal Th2Ni17-type structure for x less than or equal to 3 and the rhombohedral Th2Zn17-type struct ure for x greater than or equal to 4. Substitution of Ga for Fe in Er2 Fe17 leads to an increase of the unit-cell volume which is linear with the Ga content. The saturation magnetization at 1.5 K decreases linea rly with increasing Ga concentration. The Curie temperature is found f irst to increase, then to decrease with increasing Ga concentration, h aving a maximum value of 526 K at about x = 3. The Er2Fe17-xGax compou nds with x = 2, 3 and 4 exhibit a spin-reorientation transition with t he spin-reorientation temperature being 136, 140 and 102 K, respective ly. X-ray diffraction measurements on magnetically aligned Er2Fe17-xGa x powders show that the compounds with x less than or equal to 7 have easy-plane type of magnetic anisotropy, whereas the compound with x = 8 exhibits easy-axis type of magnetic anisotropy at room temperature. The easy-magnetization direction of the sample of x = 8 is perpendicul ar to the c-axis at low temperature. Present result demonstrates that in Er2Fe17-xGax the substitution of high concentration of Ga leads to a change in the second-order crystal field parameter A(20) from negati ve to positive. (C) 1998 Elsevier Science Ltd. All rights reserved.