Orbital-Ordering Transition in Sr{sub 2}VO{sub 4}

Temperature-dependent dc susceptibility and x-ray powder diffraction on a pure tetragonal sample of Sr{sub 2}VO{sub 4} show an antiferromagnetic orbital-ordering transition at T{sub OO}=97 K, in which the occupied orbitals lie along the c axis. The unusual broadening of the x-ray Bragg peaks throughout the orbital-ordering transition temperature region indicates that this process occurs in stages, and the onset of short-range orbital ordering occurs at T{sub 1}{approx_equal}122 K. The study of the order parameter associated with this transition by analyzing the spontaneous strain results in a critical exponent {beta}=0.35(2) consistent with 3D Heisenberg behavior. These results experimentally confirm the orbital-ordering state in Sr{sub 2}VO{sub 4} predicted by first-principles calculations using combinations of the local-density approximation and the GW method.