Magnetic studies of some orthovanadates

Abstract

The perovskites L${\mathrm{VO}}_{3}$ (L=La, Lu, or Y) are canted-spin antiferromagnets. Magnetic susceptibility measurements made on cooling from room temperature in a field of 1 kOe or on heating after cooling in 1 kOe give rise to a sample magnetization M that is oriented in opposition to the magnetizing field below 138 K in ${\mathrm{LaVO}}_{3}$, but in the direction of the magnetizing field in ${\mathrm{LuVO}}_{3}$ and ${\mathrm{YVO}}_{3}$. Orientation of the M in ${\mathrm{LaVO}}_{3}$ in opposition to the magnetizing field H occurs on cooling through a first-order magneto- strictive transition at 138 K${\mathit{T}}_{\mathit{N}}$\ensuremath{\approxeq}142 K that enhances the ${\mathit{V}}^{3+}$ ion orbital angular momentum. In ${\mathrm{YVO}}_{3}$, a first-order magnetic-order phase change at 78 K ${\mathit{T}}_{\mathit{N}}$\ensuremath{\approxeq}114 K shows no evidence of a discontinuous change in the ${\mathrm{V}}^{3+}$ ion orbital angular momentum. The same is true for a phase change in ${\mathrm{LuVO}}_{3}$ at 83 K${\mathit{T}}_{\mathit{N}}$\ensuremath{\approxeq}105 K that leaves the magnetic order unchanged. A high-pressure (P\ensuremath{\ge}8 kbar) ${\mathrm{LaVO}}_{3}$ phase metastable below 250 \ifmmode^\circ\else\textdegree\fi{}C is antiferromagnetic without spin canting. The ``anomalous diamagnetism'' previously reported for field-cooled ${\mathrm{LaVO}}_{3}$ is interpreted to reflect the first observation of a change in the direction of the persistent currents at an ion associated with a discontinuous change in an unquenched orbital angular momentum contribution to the atomic moment; a spin-orbit coupling stronger than the Zeemann coupling of the spin to the magnetizing field reverses the entire atomic moment ${\mathrm{\ensuremath{\mu}}}_{\mathit{J}}$=gJ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. Substitution of La by Lu or Y applies a chemical pressure that suppresses the first-order magnetostrictive distortion responsible for the anomalous diamagnetism.