A possible spin Jahn-Teller material: ordered pseudobrookite FeTi2O5

TL;DR

This study explores the spin-lattice coupling and potential spin Jahn-Teller effect in FeTi2O5, revealing structural distortions, magnetoelastic effects, and quantum criticality features through experimental and first-principles methods.

Contribution

It provides the first detailed investigation of spin-lattice interactions and the possible spin Jahn-Teller effect in FeTi2O5, combining experimental data with DFT+U calculations.

Findings

Antiferromagnetic transition at 42 K confirmed by magnetization and heat capacity.

Structural distortions and strong magnetoelastic coupling observed around TN.

FeTi2O5 is a quasi-1D magnet with significant single-ion anisotropy.

Abstract

We investigated the spin-lattice coupling in orthorhombic pseudobrookite FeTi2O5 single crystal with highly ordered $ Fe^{2+} / Ti^{4+}$ occupation, which consists of quasi-1D S=2 chains running along a-axis. Both the magnetization and specific heat measurements confirm that the antiferromagnetic phase transition of FeTi2O5 occurs at TN = 42 K. The structural distortions were also observed around TN in the thermal expansion $ \Delta L / L (T)$ data. Moreover, the magnetic field was found to strongly affect the thermal expansion both along chains and in the perpendicular direction clearly signaling a substantial magnetoelastic coupling, which was recently proposed to be the origin of a rare spin Jahn-Teller effect, when frustration is lifted via additional lattice distortions. Experimentally observed change in the thermal conductivity slope around TN is usually associated with the orbital ordering, but DFT+U calculations do not detect modification of the orbital structure across the transition. However, the first-principles calculation results confirm that FeTi2O5 is a quasi-1D magnet with a ratio of frustrating inter-chain to intra-chain exchanges $ J' / J = 0 . 0 3$ and a substantial single-ion anisotropy (A = 4K) of easy-axis type making this material interesting for studying quantum criticality in transverse magnetic fields.