Structural and thermodynamic properties of Fe1.12Te with multiple phase transitions

Abstract

The parent compound of iron chalcogenide superconductors, Fe1+yTe, with a range of excess Fe concentrations exhibits intriguing structural and magnetic properties. Here, the interplay of magnetic and structural properties of Fe1.12Te single crystals have been probed by low-temperature synchrotron X-ray powder diffraction, magnetization, and specific heat measurements. Thermodynamic measurements reveal two distinct phase transitions, considered unique to samples possessing excess Fe content in the range of 0.11≤y≤0.13. On cooling, an antiferromagnetic transition, TN≈57 K is observed. A closer examination of powder diffraction data suggests that the transition at TN is not purely magnetic, but accompanied by the commencement of a structural phase transition from tetragonal to orthorhombic symmetry. This is followed by a second prominent first-order structural transition at TS with TS<TN, where an onset of monoclinic distortion is observed. The results point to a strong magneto-structural coupling in this material.

Synthesis, phase stability, structural, and physical properties of 11‐type iron chalcogenides

“…More detailed low‐temperature neutron as well as SXRD experiments revealed three different types of magnetic and structural behavior in FeTe depending on the amount of excess Fe . In the compositional range , FeTe undergoes a simultaneous first‐order phase transition to a monoclinic () as well as bicollinear antiferromagnetic phase.…”

Interplay of structure, magnetism, and superconductivity in Se substituted iron telluride with excess Fe

“…Fobes et al observed that the hysteretic transition is associated to a development of bicollinear antiferromagnetic order and a ferro-orbital ordering which results in metallic transport behaviour [8]. Here, by substitution with Se the transition temperatures are altered even though the nature of the transitions appears to be preserved [7]. While T N is decreased for x = 0.02 compared to the pristine compound, T S is increased, a behaviour which is also reflected in a reduced temperature span of the transition in the sample x = 0.02.…”

“…At T N ≈ 45 K, the transition in specific heat turns into a broad hump which could either be the result of two weak transitions occurring at very close temperature or of a broad transition. Similarly, for x = 0.1, a weak hump is present near 36 K. The specific heat data of samples 0.02 ≤ x ≤ 0.10 are analyzed in detail with respect to the weak transitions: The lattice contribution is modelled using a combination of Debye and Einstein models as discussed in [7]. The model is fitted to our experimental data in the range 2 K ≤ T ≤ 275 K excluding the transition regions.…”

“…A major challenge in these studies is the precise control of the composition of the as-grown samples. For the pristine compound, the composition was determined to Fe 1.12 Te by using synchrotron X-ray diffraction [7]. All other compositions were estimated by employing the EPMA technique.…”

“…At lower temperature, the above transition is followed by a first-order transition (identified as T S ). At this second phase transition, the crystal symmetry changes to a monoclinic phase [6,7] and the incommensurate AFM structure becomes commensurate [3]. Thus, both the phase transitions consist of structural as well as magnetic components.…”