Competing spin density wave, collinear, and helical magnetism inFe1+xTe

Abstract

The Fe 1+x Te phase diagram consists of two distinct magnetic structures with collinear order present at low interstitial iron concentrations and a helical phase at large values of x with these phases separated by a Lifshitz point. We use unpolarized single-crystal diffraction to confirm the helical phase for large interstitial iron concentrations and polarized single-crystal diffraction to demonstrate the collinear order for the iron-deficient side of the Fe 1+x Te phase diagram. Polarized neutron inelastic scattering shows that the fluctuations associated with this collinear order are predominately transverse at low-energy transfers, consistent with a localized magnetic moment picture. We then apply neutron inelastic scattering and polarization analysis to investigate the dynamics and structure near the boundary between collinear and helical orders in the Fe 1+x Te phase diagram. We first show that the phase separating collinear and helical orders is characterized by a spin density wave with a single propagation wave vector of (∼0.45, 0, 0.5). We do not observe harmonics or the presence of a charge density wave. The magnetic fluctuations associated with this wave vector are different from the collinear phase, being strongly longitudinal in nature and correlated anisotropically in the (H,K) plane. The excitations preserve the C 4 symmetry of the lattice but display different widths in momentum along the two tetragonal directions at low-energy transfers. While the low-energy excitations and minimal magnetic phase diagram can be understood in terms of localized interactions, we suggest that the presence of the density wave phase implies the importance of electronic and orbital properties.

Phonon spectra in the parent superconducting iron-tuned telluride Fe1+xTe from inelastic neutron scattering and ab initio calculations

“…Extending INS to polarized neutron measurements offers a robust perspective offering the possibility to explore directly and unambiguously the spinphonon coupling picture in iron telluride. In this context, the anisotropic nature of different types of low-temperature magnetic fluctuations were probed in iron telluride Fe1+xTe [60], confirming further the importance of magnetoelastic coupling. A next step could be the use of this same technique to draw a complete picture of both the lattice and the spin components in these materials.…”

Evidence of the Plaquette Structure of Fe1+xTe Iron Telluride: Mössbauer Spectroscopy Study

“…The low‐temperature Mössbauer spectrum of the Fe 1.05 Te system consisted of four magnetic sextets, which were a consequence of four iron ion groups . For the Fe 1.125 Te system, a more complex low temperature spectrum is expected because of the presence of spin density waves . It was reported that the magnetic structure of Fe 1.124(5) Te (notations of ref.…”

“…It was reported that the magnetic structure of Fe 1.124(5) Te (notations of ref. ) is a collinear spin density wave (SDW) phase with incommensurate wave‐vector q = 0.46 ± 0.01 (in reciprocal‐lattice units (r.l.u. )) along [ H ,0,0] direction (that corresponds to the x ‐direction in real space).…”

“…. Moreover, the existence of three distinct regions in the phase diagram of magnetic ordering in dependence on the excess‐iron concentration could be a result of the above‐mentioned three regimes of the plaquette arrangement.…”

“…Contrary to the expectations, superconductivity has not been observed in the stoichiometric iron telluride compound. Moreover, it is well known that iron telluride is always synthesized with iron off‐stoichiometry – a feature, which attracts very much attention last time (see recent work and references therein). In our previous study, the off‐stoichiometric iron telluride Fe 1.05 Te was studied making use of a combination of Mössbauer spectroscopy experiments and ab initio calculations.…”