Structural anomalies and short-range magnetic correlations in the orbitally degenerate systemSr2VO4

We report on the electronic ground state of a layered perovskite vanadium oxide ${\mathrm{Sr}}_{2}{\mathrm{VO}}_{4}$ studied by the combined use of synchrotron radiation x-ray diffraction (SR-XRD) and muon spin rotation/relaxation $(\ensuremath{\mu}\mathrm{SR})$ techniques, where $\ensuremath{\mu}\mathrm{SR}$ measurements were extended down to 30 mK. We found an intermediate orthorhombic phase between ${T}_{\mathrm{c}2}\ensuremath{\sim}130$ K and ${T}_{\mathrm{c}1}\ensuremath{\sim}100$ K, whereas a tetragonal phase appears for $Tg{T}_{\mathrm{c}2}$ and $Tl{T}_{\mathrm{c}1}$. The absence of long-range magnetic order was confirmed by $\ensuremath{\mu}\mathrm{SR}$ at the reentrant tetragonal phase below ${T}_{\mathrm{c}1}$, where the relative enhancement in the $c$-axis length versus that of the $a$-axis length was observed. However, no clear indication of the lowering of the tetragonal lattice symmetry with superlattice modulation, which is expected in the orbital order state with superstructure of ${d}_{yz}$ and ${d}_{zx}$ orbitals, was observed by SR-XRD below ${T}_{\mathrm{c}1}$. Instead, it was inferred from $\ensuremath{\mu}\mathrm{SR}$ that a magnetic state developed below ${T}_{\mathrm{c}0}\ensuremath{\sim}10$ K, which was characterized by the highly inhomogeneous and fluctuating local magnetic fields down to 30 mK. We argue that the anomalous magnetic ground state below ${T}_{\mathrm{c}0}$ originates from the coexistence of ferromagnetic and antiferromagnetic correlations.