Structural and magnetic phase transitions of the orthovanadatesRVO3(R=Dy, Ho, Er) as seen via neutron diffraction

The structural and magnetic phase behavior of $R$VO${}_{3}$ with $R$$=$v Dy, Ho, and Er was studied by single-crystal neutron diffraction. Upon cooling, all three compounds show structural transitions from orthorhombic (space group Pbnm) to monoclinic ($p$2${}_{1}$/$b$) symmetry due to the onset of orbital order at $T$$=$ 188--200 K, followed by N\'eel 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 ${\mathrm{V}}^{3+}$ 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${}_{3}$.