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 $(\mu \mathrm{SR})$ techniques, where $\mu \mathrm{SR}$ measurements were extended down to 30 mK. We found an intermediate orthorhombic phase between $T_{\mathrm{c}2}\sim 130$ K and $T_{\mathrm{c}1}\sim 100$ K, whereas a tetragonal phase appears for $T>T_{\mathrm{c}2}$ and $T<T_{\mathrm{c}1}$. The absence of long-range magnetic order was confirmed by $\mu \mathrm{SR}$ 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 $\mu \mathrm{SR}$ that a magnetic state developed below $T_{\mathrm{c}0}\sim 10$ 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.

• Received 31 May 2015
• Revised 13 July 2015

DOI:https://doi.org/10.1103/PhysRevB.92.064408