A canted-spin ferromagnetic moment $\mathbf{M}$ parallel to the orthorhombic ($Pbnm$) $a$ axis of a $\mathrm{Y}\mathrm{V}{\mathrm{O}}_3$ single crystal changes sign from the direction of a measuring field $\mathbf{H}⩽1\mathrm{kOe}$ on warming from $5\mathrm{K}$ across a first-order orbital-spin reordering temperature $T_{CG}$; the magnetization changes sign again on warming across $T^{*}$ in the interval $T_{CG}<T^{*}<T_N$, where $T_N$ is the antiferromagnetic Néel temperature. Although the magnitude of $\mathbf{M}$ and its sign changes are the same for a sample cooled in a measuring field (FC) and zero-applied field (ZFC) to $5\mathrm{K}$, the $\mathbf{M}\left(T\right)$ curves differ for warming after FC and ZFC to just above $T_{CG}$; but the sign reversal of $\mathbf{M}$ occurs at the same $T^{*}$ with the same measuring field $\mathbf{H}$. These unusual features are argued to be the result of two coupled spin-canting mechanisms that oppose one another, an antisymmetric exchange operating on a $c$-axis spin component, and a 90° site anisotropy in the $a\text{−}b$ plane operating on a $b$-axis component of the spin. The relative strength of the antisymmetric exchange increases with decreasing $\mathrm{V}\mathrm{O}\mathrm{V}$ bond angle to give a $T^{*}$ close to a $T_{OO}\approx T_N$ in $\mathrm{La}\mathrm{V}{\mathrm{O}}_3$ and no $T^{*}$ above $T_{CG}$ in $\mathrm{Lu}\mathrm{V}{\mathrm{O}}_3$.

• Received 20 April 2005

DOI:https://doi.org/10.1103/PhysRevB.72.094412