MODULATED MAGNETIC-STRUCTURES IN UPD2GE2

Neutron diffraction study of polycrystalline UPd2Ge2 compound with the tetragonal body centered ThCr2Si2-type crystal structure shows succes sive modulated magnetic phases below T-N similar or equal to 135 K. Fo r T less than or equal to 80 K, the propagation wave-vector k is locke d to the commensurate value k=(0,0,k(z)=3/4); for T>80 K k(z) becomes incommensurate varying with temperature from 0.75 to similar to 0.717 at 130 K. For T<50 K, the magnetic structure is well approximated by a squared modulation; above 50 K it transforms continuously up to 95 K where it becomes purely sinusoidal. Below T-N, the uranium magnetic mo ments are always parallel to the tetragonal c-axis.