MAGNETIC-ORDERING OF RNISB2 (R=PR, ND AND TB) COMPOUNDS STUDIED BY NEUTRON-DIFFRACTION AND MAGNETIC MEASUREMENTS

Results of X-ray, neutron diffraction and magnetic measurements for RN iSb2 (R=Pr, Nd and Tb) compounds are presented. All compounds crystall ize in the tetragonal CaBe2Ge2-type crystal structure and are antiferr omagnets with the Neel temperature 6.3 K for R=Pr, 2.3 K for R=Nd and 12 K for R=Tb. Below T-N a colinear antiferromagnetic structure of the AFI type is observed for R=Nd, a square modulated structure with the wavevector k=(0, 0, 0.25) for R=Pr and a square and sine modulated wit h the wavevector k=(k(x), k(y), 0) for R=Tb. For R=Pr, Nd and Tb compo unds the magnetic moments of the rare earth atoms are parallel to c-ax is. The obtained data are analyzed in terms of the exchange interactio ns theory and crystal electric field.