Magnetic structure of HoPd2Si2 redefined on the basis of new neutron diffraction data

A new sample of HoPd2Si2 (ThCr2Si2-type structure, space group I4/mmm) has been prepared and investigated. Magnetic susceptibility and magnetization d ata 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 describ ed in an enlarged magnetic unit cell (a(m) = 7a, b(m) = a and c(m) = 6c), i s observed. A complex magnetic structure of sine-wave modulated type with t wo propagation vectors and Ho magnetic moments parallel to the b-axis is pr oposed. 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.