NEUTRON-DIFFRACTION STUDIES OF METAMAGNETIC PHASE-TRANSITIONS IN TBRU2SI2 AND DYRU2SI2

Investigations of metamagnetic phase transitions in TbRu2Si2 and DyRu2Si2 using single-crystal neutron diffraction under magnetic fields up to 5 T along the c-axis are reported. Without a magnetic field, TbRu2Si2 and DyRu2Si2 exhibit a one-dimensional magnetic order of a squared wave with a wavevector tau = (0.23, 0, 0) and tau = (0.222, 0, 0) respectively, with magnetic moments parallel or antiparallel to the c axis. The tau = 0.23 wave consists of 26 ferromagnetic (100) planes with a 5+4-4+5-4+4- sequence along the a axis, where 5+ and 4- denotes five and four consecutive ferromagnetic (100) planes with up and down spins respectively. The tau = 0.222 structure can be expressed by a 5+5-4+4- sequence. Applied fields induce a gradual change in this one-dimensionality up to a critical field H(c1) = 21 kOe; from this value up to H(c2) = 29 kOe, TbRu2Si2 becomes a two-dimensionally modulated ferrimagnet with the wavevectors (0.23, 0, 0), (0.23, 0.23, 0) and a ferromagnetic component. Just below H(c1) the structure becomes ferrimagnetic with a 5+4-5+3-5+4- sequence. Above H(c2) = 29 kOe all the moments are ferromagnetically aligned in the field direction. DyRu2Si2 shows a similar metamagnetic behaviour with H(c1) = 10 kOe and H(c2) = 17 kOe. The metamagnetic phase is two dimensional with wavevectors (0.222, 0, 0), (0.222, 0.222, 0) and a ferromagnetic component.