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Abstract:
The structural and magnetic phase behavior of RVO(3) with R = Dy, Ho, and Er was studied by single-crystal neutron diffraction. Upon cooling, all three compounds show structural transitions from orthorhombic (space group Pbnm) to monoclinic (P2(1)/b) symmetry due to the onset of orbital order at T = 188-200 K, followed by Neel transitions at T = 110-113 K due to the onset of antiferromagnetic (C-type) order of the vanadium moments. Upon further cooling, additional structural phase transitions occur for DyVO(3) and ErVO(3) at 60 and 56 K, respectively, where the monoclinic structure changes to an orthorhombic structure with the space group Pbnm, and the magnetic order of the V sublattice changes to a G-type structure. These transition temperatures are reduced compared to the ones previously observed for nonmagnetic R(3+) ions due to exchange interactions between the V(3+) and R(3+) ions. For ErVO(3), R-R exchange interactions drive a transition to collinear magnetic order at T = 2.5 K. For HoVO(3), the onset of noncollinear, weakly ferromagnetic order of the Ho moments nearly coincides with the structural phase transition from the monoclinic to the low-temperature orthorhombic structure. This transition is characterized by an extended hysteresis between 24 and 36 K. The Dy moments in DyVO(3) also exhibit noncollinear, weakly ferromagnetic order upon cooling below 13 K. With increasing temperature, the monoclinic structure of DyVO(3) reappears in the temperature range between 13 and 23 K. This reentrant structural transition is associated with a rearrangement of the Dy moments. A group theoretical analysis showed that the observed magnetic states of the R(3+) ions are compatible with the lattice structure. The results are discussed in the light of recent data on the magnetic field dependence of the lattice structure and magnetization of DyVO(3) and HoVO(3).
