ANOMALOUS MAGNETIC-PROPERTIES OF DYRU2SI2

DyRu2Si2 has a high-order commensurate structure with a wavevector Q=( 2/9,0,0) below T-N=29K and shows anomalous magnetic behavior around T- t = 3.5 K. Molecular geld calculations of the free energy, magnetic mo ments, magnetic susceptibility and specific heat have been made in an attempt to understand better the nature of the magnetism. The magnetis m is understandable by a model that the compound undergoes a phase cha nge at T-t to a high temperature phase in which paramagnetic planes ap pear every ninth (200) plane of the body centered tetragonal structure . The appearance of the paramagnetic planes is attributable to the fea ture of the wave-dependent molecular field coefficient lambda(q(x)) wh ich takes a pronounced maximum at q(x) = 2/9 and negative values for a wide range of 4/9 less than or equal to q(x) less than or equal to 1.