Magnetic structure of HoPd2Si2redefined on the basis of new neutron diffraction data

A new sample of HoPd 2 Si 2 (ThCr 2 Si 2 -type structure, space group I 4/ mmm ) has been prepared and investigated. Magnetic susceptibility and magnetization data indicate antiferromagnetic behaviour below T N = 5.8 K. On the basis of powder neutron diffraction data the magnetic structure of the compound has been redefined and found to be more complex than reported earlier. In the temperature region from 20 K to 5 K a short-range magnetic order develops. Between 1.5 K and 5 K a long-range magnetic ordering, that could be described in an enlarged magnetic unit cell ( a m = 7 a , b m = a and c m = 6 c ), is observed. A complex magnetic structure of sine-wave modulated type with two propagation vectors and Ho magnetic moments parallel to the b -axis is proposed. Moreover, a new attempt to understand the transition from long- to short-range magnetic ordering observed in some rare earth compounds with Pd is made.