MAGNETIC-STRUCTURES OF RNI(2)GE(2) (R=DY, HO AND ER) AND YBNI2SI2

Results of X-ray, neutron diffraction, Mossbauer effect and magnetometric measurements for RNi(2)Ge(2) (R = Dy, Ho and Er) and YbNi2Si2 compounds are presented. All compounds crystallize in the tetragonal ThCr2Si2 (CeAl2Ga2)-type crystal structure and are antiferromagnets with the Neel temperature of 7.5 K for R =Dy, 4.8 K for R = Ho and 3.65 K for R = Er and 2.3 K for YbNi2Si2. Below T-N a sinemodulated structure with k = (0, 0, k(z)) is observed for RNi(2)Ge(2) compounds (R = Dy and Er) and with k = (k(x), k(y), k(z)) for HoNi2Ge2. The YbNi,Si, has a helicoidal ordering confirmed by the Mossbauer effect data. The Ni atom is non-magnetic and rare earth moments form an angle phi with the c-axis which changes from 20 degrees for R = Dy to 90 degrees for YbNi2Si2. The obtained data are analyzed in terms of the RKKY theory and crystal electric field.