A possible spin Jahn-Teller material: ordered pseudobrookite FeTi2O5

Abstract

We investigated the spin-lattice coupling in orthorhombic pseudobrookite FeTi2O5 single crystal with highly ordered $F{e}^{2+}/T{i}^{4+}$ 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 $J^{\prime }/J=0.03$ and a substantial single-ion anisotropy (A = 4K) of easy-axis type making this material interesting for studying quantum criticality in transverse magnetic fields.

20 pages, 7 figures

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Cited by in corpus (1)

• Elastic softness of low-symmetry frustrated $A$Ti${}_2$O${}_5$ ($A$ = Co, Fe)