Magnetic structures of Y6(Fe1-xAlx)23compounds

Neutron diffraction studies of three Y6(Fe1-xAlx)23compounds (x = 0.05, 0.10, 0.15) at 523K and 77K reveal substantial preferential atomic ordering of Fe and Al atoms on the four transition metal crystallographic sites. Fe atoms prefer to occupy the f1site and Al atoms the f2site. The site preferences are explained on the basis of the comparative atomic volumes and the nearest neighbor distances. At 77K the compounds are ferromagnetic. The moments of the Fe atoms lie along the <111> direction and exhibit different magnetic moments on the four transition metal crystallographic sites. The decrease in the Curie temperature and magnetization of Y6Fe23with increasing Al content arises as a result of two effects, dilution of the Fe sublattice with nonmagnetic atoms and changes in the preferential atomic ordering which govern the local environments of the Fe atoms so as to decrease the average Fe moment.