Crystallographic phase coexistence, spin-orbital order transitions, and spontaneous spin flop inTmVO3

The thermal evolution of structural and magnetic details of the orthovanadate $\mathrm{TmV}{\mathrm{O}}_{3}$, studied in detail by neutron and synchrotron powder diffraction, is reported. Crystallizing in space group Pnma at room temperature, $\mathrm{TmV}{\mathrm{O}}_{3}$ undergoes a first structural phase transition to $P{2}_{1}/a$ at ${T}_{\mathrm{OO}}=180\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, where a $G$-type orbital ordered state develops. At ${T}_{\mathrm{S}}=75\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, a change back to Pnma occurs, and the establishment of $C$-type orbital order takes place. The ${\mathrm{V}}^{3+}$ ions order antiferromagnetically with a magnetic propagation vector $\mathbf{k}=0$ below ${T}_{\mathrm{N}1}=105\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, while the $\mathrm{T}{\mathrm{m}}^{3+}$ sublattice orders at ${T}_{\mathrm{N}2}=20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ following the same propagation vector. Between ${T}_{\mathrm{N}1}$ and ${T}_{\mathrm{S}}$, a coexistence of $G$-type ($P{2}_{1}/a$) and $C$-type (Pnma) orbital ordered states exists. The $P{2}_{1}/a$ phase is magnetically separated into two fractions, which adopt a ${C}_{x}{C}_{y}0$ and ${G}_{x}00$ coupling, respectively, while the Pnma volume fraction follows a $0{G}_{y}0$ magnetic structure. At ${T}_{\mathrm{N}2}$, the appearance of the Tm sublattice magnetization ($0{C}_{y}0$) leads to a spin flop transition of the V sublattice from $0{G}_{y}0$ to ${G}_{x}00$. The results are presented and analyzed in the general context of the series of $R\mathrm{V}{\mathrm{O}}_{3}$ compounds, and they are used to discuss recent magnetization results.