FeTi2O5 : 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 FeTi2O5. We observe a long range ordered state below TN=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 k=(1/2,1/2,0) reported for CoTi2O5 (TN=26 K). By comparing our data with calculated dipolar fields we can restrict the possible moment size and directions of the Fe 2+ ions. arXiv:1906.06219v2 [cond-mat.str-el]

Ab initio modeling and experimental investigation of Fe2P by DFT and spin spectroscopies

“…In order to further characterize the microscopic origin of the experimental results and to validate ab initio estimates of hyperfine couplings, we evaluated the internal field at P and the muon sites, after having identified the interstitial position occupied by the latter following a methodology already extensively discussed [42][43][44][45][46][47][48][49][50][51]. Five inequivalent candidate muon sites, labeled with letters from A to E in order of increasing total energy, are reported in Table I.…”

The quantum muon

“…Sometimes the muon signal can be remarkably complex, such as found in the chargeordered triangular antiferromagnet AgNiO 2 which exhibits six distinct muon precession signals [24]. Muon data have also been pivotal in identifying spin Jahn-Teller antiferromagnetism in compounds where a magnetically-driven lattice distortion is necessary for establishing magnetic order [25,26]. Although neutron diffraction remains the technique of choice for identifying magnetic ground states [27], µSR is particularly effective when the ordered moment is weak and arises from an element that hinders neutron measurements, such as osmium [28,29] or iridium [30,31].…”

DFT + μ: Density functional theory for muon site determination

“…In this case the site is consistent with the dipole-field map computed for the known magnetic structure, giving confidence that the DFT-derived site is likely the one realised. Other ionic systems in which DFT+µ calculations show that the muon occupies a site close to the anion include the honeycomb system 56 and the spin-Jahn-Teller antiferromagnets 57,58 CoTi 2 O 5 and FeTi 2 O 5 . A similar approach applies in the case of the ferromagnet Nd 2 Fe 14 B, where the muon site is identified [the 8i site (0.6745,0.8838,0)] near the square base of a NdFe 3 B pyramid, leading to a quantitative measurement (using the observed µSR precession frequencies) of the moment on the Nd and Fe atoms.…”