Optical and magneto-optical properties of ${\mathrm{YVO}}_3$ single crystal were studied in the far-infrared, visible, and ultraviolet regions. Two structural phase transitions at 75 K and 200 K were observed and established to be of first and second order, respectively. The lattice has an orthorhombic Pbnm symmetry both above 200 K as well as below 75 K and is found to be either dimerized monoclinic $\mathrm{Pb}11\mathrm{}$ or triclinic $P1\mathrm{}¯$ in between. We identify ${\mathrm{YVO}}_3$ as a Mott-Hubbard insulator with an optical gap of 1.6 eV. The visible spectrum shows three d-band excitations at 1.8, 2.4, and 3.3 eV, followed by charge-transfer transitions at about 4 eV. The observed structure is in good agreement with LSDA+U band structure calculations. By using ligand field considerations, we assigned these bands to the transitions to the ${}^4{A}_{2g},$ ${}^2{E}_g{+}^2{T}_{1g},$ and ${}^2{T}_{2g}$ states. The strong temperature dependence of these bands is in agreement with the formation of orbital order. Despite the small net magnetic moment of $0.01{\mu }_B$ per vanadium, a Kerr effect of the order of $0.01°$ was observed for all three d bands in the magnetically ordered phase ${(T}_{\mathrm{N}\mathrm{é}\mathrm{el}}=116\mathrm{}\mathrm{K}).\mathrm{}$ A surprisingly strong enhancement of the Kerr effect was found below 75 K, reaching a maximum of $0.1°.$ This effect is ascribed to the nonvanishing net orbital magnetic moment.

• Received 8 April 2003

DOI:https://doi.org/10.1103/PhysRevB.69.075110