Structural and magnetic properties of R-2(Fe,Si)(17) compounds with R=Tb and Er

The structural and magnetic properties of R2F17-xSix compounds have been in vestigated by means of X-ray diffraction and magnetization measurements. Su bstitution of Si for Fe leads to a clear reduction of the unit-cell volume. With increasing Si content, a phase transition from the Th2Ni17- to the Th 2Zn17-type of structure has been observed for R=Tb, while all compounds cry stallize in the Th2Ni17-type of structure for R=Er. A clear decrease of the saturation moment and an increase of the Curie temperature have been found upon Si substitution. The exchange-interaction constant J(TbFe) between th e Tb and the Fe moments has been obtained from a mean-field analysis of the Curie temperature T-c. The X-ray diffraction patterns of magnetically-alig ned powder samples show that the easy magnetization direction is in the pla ne for all compounds investigated. (C) 1999 Elsevier Science S.A, All right s reserved.