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

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 $T_{\mathrm{N}}$=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 $\mathbf{k}$=(1/2,1/2,0) reported for CoTi${}_2$O${}_5$ ($T_{\mathrm{N}}$=26 K). By comparing our data with calculated dipolar fields we can restrict the possible moment size and directions of the Fe${}^{2+}$ ions.