Neutron diffraction and magnetic studies of Nd/sub 2/Fe/sub 17-x/T/sub x/ (T=Si, Mn) alloys

We have carried out neutron and magnetic studies on Nd/sub 2/Fe/sub 17-x/T/sub x/ (T=Si, Mn) alloys. The unit cell of the compounds contracts with both Si and Mn substitution. Si atoms avoid the 6c site, prefer the 18h site strongly, fill the 9d site steadily and fill the 18f site only at relatively high Si concentration. Mn atoms avoid the 9d sites but prefer the 6c site strongly, while the 18f site and 18h site fill slowly. The Si site occupancies appear to be dominated by the crystal environment while the Mn site occupancies are dominated by steric considerations. The Curie temperature of the compound Nd/sub 2/Fe/sub 17/ increases significantly with Si substitution but is only affected slightly by the Mn substitution. Although the unit cell contracts with increasing Si concentration, the average length of bonds to the Fe(6c) and the Fe(18f) sites increase slightly at x<4.