NEUTRON-DIFFRACTION AND MAGNETIC STUDIES OF ND2FE17-XTX (T=SI, MN) ALLOYS

We have carried out neutron and magnetic studies on Nd2Fe17-T-x(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 Ish site s trongly, fill the 9d site steadily and fill the 18f site only at relat ively high Si concentration. Mn atoms avoid the 9d sites but prefer th e 6c site strongly, while the 18f site and 18h site fill slowly. The S i site occupancies appear to be dominated by the crystal environment w hile the Mn site occupancies are dominated by steric considerations. T he Curie temperature of the compound Nd2Fe17 increases significantly w ith Si substitution but is only affected slightly by the Mn substituti on. Although the unit cell contracts with increasing Si concentration, the average length of bonds to the Fe(6c) and the Fe(18f) sites incre ase slightly at x<4.