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 RNiSb2 (R=Pr, Nd and Tb) compounds are presented. All compounds crystallize in the tetragonal CaBe2Ge2-type crystal structure and are antiferromagnets 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 with the wavevector k=(k(x), k(y), 0) for R=Tb. For R=Pr, Nd and Tb compounds the magnetic moments of the rare earth atoms are parallel to c-axis. The obtained data are analyzed in terms of the exchange interactions theory and crystal electric field.