We investigated the spin-lattice coupling in orthorhombic pseudobrookite FeTi2O5 single crystal with highly ordered Fe2+/Ti4+ 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 ΔL/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=0.03 and a substantial single-ion anisotropy (A = 4K) of easy-axis type making this material interesting for studying quantum criticality in transverse magnetic fields.
@article{arxiv.2405.19625,
title = {A possible spin Jahn-Teller material: ordered pseudobrookite FeTi2O5},
author = {Hao-Hang Xu and Jian Liu and L. L. Tao and Xian-Jie Wang and Sergey V. Streltsov and Yu Sui},
journal= {arXiv preprint arXiv:2405.19625},
year = {2024}
}