Structural anomalies and short-range magnetic correlations in the orbitally degenerated system Sr$_2$VO$_4$

TL;DR

This study investigates the electronic and magnetic ground states of Sr$_2$VO$_4$, revealing structural phase transitions, absence of long-range magnetic order in certain phases, and the emergence of a complex magnetic state at very low temperatures.

Contribution

It provides detailed insights into the structural anomalies and short-range magnetic correlations in Sr$_2$VO$_4$, highlighting the coexistence of ferromagnetic and antiferromagnetic interactions.

Findings

Intermediate orthorhombic phase between 100-130 K

No long-range magnetic order below 10 K

Development of inhomogeneous magnetic state at low temperatures

Abstract

We report on the electronic ground state of a layered perovskite vanadium oxide Sr$_2$VO$_4$ studied by the combined use of synchrotron radiation x-ray diffraction (SR-XRD) and muon spin rotation/relaxation ($\mu$SR) techniques, where $\mu$SR measurements were extended down to 30 mK. We found an intermediate orthorhombic phase between $T_{\rm c2} \sim$~130 K and $T_{\rm c1} \sim$~100 K, whereas a tetragonal phase appears for $T > T_{\rm c2}$ and $T < T_{\rm c1}$. The absence of long-range magnetic order was confirmed by $\mu$SR at the reentrant tetragonal phase below $T_{\rm c1}$, 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 $T_{\rm c1}$. Instead, it was inferred from $\mu$SR that a magnetic state developed below $T_{\rm c0} \sim$~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 $T_{\rm c0}$ originates from the coexistence of ferromagnetic and antiferromagnetic correlations.