ANOMALOUS LOW-TEMPERATURE MAGNETIC-BEHAVIOR IN DYRU2SI2 AND DYRU2GE2

The body-centred tetragonal compounds DyRu2Si2 and DyRu2Ge2 order with in a collinear modulated magnetic structure at T-N = 29 and 22 K, resp ectively. Below similar to 5 K, both compounds present a low-field low -temperature magnetic state which exhibits several nonconventional fea tures. The most spectacular one is a double-peak structure in the temp erature dependence of the specific heat, associated with a giant varia tion of the magnetic entropy. Other anomalous characteristics include an unexpected change of behaviour in the magnetization processes and a n unusual variation of the resistivity in this temperature range. The nature of this low-temperature phase is a puzzle.