Structural and magnetic properties of R2(Fe,Si)17 compounds with R=Tb and Er

The structural and magnetic properties of R2Fe17-xSix compounds have been investigated by means of X-ray diffraction and magnetization measurements. Substitution 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 Th2Zn17-type of structure has been observed for R=Tb, while all compounds crystallize 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 JTbFe between the Tb and the Fe moments has been obtained from a mean-field analysis of the Curie temperature Tc. The X-ray diffraction patterns of magnetically-aligned powder samples show that the easy magnetization direction is in the plane for all compounds investigated. (orig.)