# FeTi$_2$O$_5$: a spin Jahn-Teller transition enhanced by cation substitution

## TL;DR

This study investigates the magnetic and crystal structure of FeTi$_2$O$_5$ using multiple experimental and theoretical methods, revealing a spin Jahn-Teller driven antiferromagnetic order below 41.8 K.

## Contribution

It provides the first detailed analysis of FeTi$_2$O$_5$'s magnetic structure, demonstrating a spin Jahn-Teller transition enhanced by cation substitution.

## Key findings

- Long-range magnetic order below 41.8 K.
- Evidence of spin Jahn-Teller effect in FeTi$_2$O$_5$.
- Constraints on Fe$^{2+}$ magnetic moments.

## Abstract

We have used muon-spin rotation, heat capacity and x-ray diffraction measurements in combination with density functional theory and dipole field calculations to investigate the crystal and magnetic structure of FeTi$_2$O$_5$. We observe a long range ordered state below $T_{\rm N}$=41.8(5) K with indications of significant correlations existing above this temperature. We determine candidate muon stopping sites in this compound, and find that our data are consistent with the spin Jahn-Teller driven antiferromagnetic ground state with $\boldsymbol{k}$=(1/2,1/2,0) reported for CoTi$_2$O$_5$ ($T_{\rm N}$=26 K). By comparing our data with calculated dipolar fields we can restrict the possible moment size and directions of the Fe$^{2+}$ ions.