Structural anomalies and short-range magnetic correlations in the orbitally degenerate system Sr2VO4

We report on the electronic ground state of a layered perovskite vanadium oxide Sr2VO4 studied by the combined use of synchrotron radiation x-ray diffraction (SR-XRD) and muon spin rotation/relaxation (μSR) techniques, where μSR measurements were extended down to 30 mK. We found an intermediate orthorhombic phase between Tc2∼130 K and Tc1∼100 K, whereas a tetragonal phase appears for T>Tc2 and T<Tc1. The absence of long-range magnetic order was confirmed by μSR at the reentrant tetragonal phase below Tc1, 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 dyz and dzx orbitals, was observed by SR-XRD below Tc1. Instead, it was inferred from μSR that a magnetic state developed below Tc0∼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 Tc0 originates from the coexistence of ferromagnetic and antiferromagnetic correlations.