Magnetic studies of some orthovanadates

The perovskites LVO₃ (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 LaVO₃, but in the direction of the magnetizing field in LuVO₃ and YVO₃. Orientation of the M in LaVO₃ in opposition to the magnetizing field H occurs on cooling through a first-order magneto- strictive transition at 138 KTN{}142 K that enhances the V³⁺ ion orbital angular momentum. In YVO₃, a first-order magnetic-order phase change at 78 K TN{}114 K shows no evidence of a discontinuous change in the V³⁺ ion orbital angular momentum. The same is true for a phase change in LuVO₃ at 83 KTN{}105 K that leaves the magnetic order unchanged. A high-pressure (P{≥}8 kbar) LaVO₃ phase metastable below 250 ^∘{}C is antiferromagnetic without spin canting. The ``anomalous diamagnetism'' previously reported for field-cooled LaVO₃ 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 μJ=gJμB. Substitution of La by Lu or Y applies a chemical pressure that suppresses the first-order magnetostrictive distortion responsible for the anomalous diamagnetism.