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Neutron diffraction, magnetization and Mossbauer spectroscopic studies of the magnetic properties of Nd(2)Fe(17-x)Al(x) solid solutions indicate that knowledge of the site occupancies of aluminium is essential for the proper characterization of the effect of exchange pathways in solid solutions. The aluminium atoms select 18f and 6c sites at high aluminium concentrations, or the 18h site after removal from 9d site. Increase in aluminium levels reduces the weighted average decremental field while neighboring shell enhances the wavelength of Friedel oscillations.

R(sub2)Fe(sub17) is a common intermetallic phase with magnetic properties than can be altered by replacing part of the iron with another metal. The Mossbauer spectra of several rhombohedral Tb(sub2)Fe(sub17-x)Six solid solutions have been measured as a function of temperature. Temperature changes occurred on cooling to 85 K. Reasonable hyperfine parameters and expected changes in temperature were seen.

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

Mossbauer spectroscopy and neutron diffraction study the magnetic properties of Tb2Fe(17-x)Alx type solid solutions. Neutron-diffraction data show a decrease in magnetic moment with values of x greater than four. Mossbauer spectra indicate that these solid solutions are ferromagnetically ordered at 85 K. A rise in x and lowering of temperature causes spin reorientation. Isomer shifts also increase due to the increase in x.

We have studied the magnetic properties of the rhombohedral [Ce.sub.2][Fe.sub.17-x][Al.sub.x]([N.sub.y]) compounds. Aluminum substitution in [Ce.sub.2][Fe.sub.17] leads to ferromagnetism for medium Al concentration and to cluster glasses for high Al concentration. The Curie temperature shows a maximum. Rare-earth nitrides of the composition [Ce.sub.2][Fe.sub.17-x][Al.sub.x][N.sub.y] can be prepared by the reaction of [Ce.sub.2][Fe.sub.17-x][Al.sub.x] with nitrogen gas at 500 [degrees] C. The crystal structure and lattice constants have been determined for all compounds. The Curie temperature enhances upon nitrogenation. The nitrogen absorption capacity decreases with composition x and vanishes for x > 5. The enhancement of the Curie temperature of the nitrides decreases according to the absorption capacity.