Evolution of two-step structural phase transition in Fe1+Te detected by low-temperature x-ray diffraction

Abstract

The low-temperature crystal structure of Fe1.13Te, which exhibits an anomalous two-step magnetic transition, was clarified by the systematic x-ray diffraction measurements. It was found that two-step structural phase transition, tetragonal-orthorhombic-monoclinic, occurred correspondingly to the two-step magnetic transition. The detailed analysis of the profile at 5 K indicated the coexistence of the minor orthorhombic area inside the major monoclinic lattice, which could explain the lower-shift (suppression) of the antiferromagnetic transition temperature in Fe1.13Te and suggest a possibility of superconductivity at the domain boundary.

Low-temperature phase diagram of Fe1+yTe studied using x-ray diffraction

“…For Fe 1.13 Te, a two-phase refinement of the diffraction pattern taken at 34 K also gives minimum R values for relative fractions of 65% monoclinic and 35% orthorhombic phases. According to Mizuguchi et al, for 1.13 Te the estimated population of the orthorhombic phase at 5 K is 20%-30%, which is close to our results at 10 K. 15 At a higher Fe content, y = 0.14, the broadening of the (200) peak appears at 54 K and visible splitting is monitored at around 50 K (Fig. 10).…”

“…Previously reported excess amounts of iron in tetragonal Fe 1+y Te ranged from 0% to 30%. 12,15,[20][21][22] According to our x-ray diffraction study and lattice parameters represented in Figs. 1(a) and 1(b), the homogeneity range of tetragonal Fe 1+y Te is clearly smaller than those given in these previous reports.…”

“…In the case of Fe 1.13 Te, we reported two thermodynamic anomalies, and assigned the phase transition at lower temperature T s = 46 K to the structural transformation. 14 However, a recent report 15 on the same nominal composition by Mizuguchi et al shows a two-step structural phase transition, from a tetragonalorthorhombic followed by an orthorhombic-monoclinic structure upon cooling. Further, the neutron diffraction data on Fe 1.10 Te with similar thermodynamic properties such as our Fe 1.13 Te indicated a structural anomaly at 63 K followed by a long-range magnetic order at 57.5 K. These different results may also be related to subtle differences in the Fe content.…”

“…9 Following this report, several other groups made similar observations. [12][13][14][15] However, due to the extreme sensitivity of the physical properties of Fe 1+y Te to the amount of y, it is often difficult to compare the results of independent measurements. Furthermore, Rodriguez et al reported a phase diagram 12 of Fe 1+y Te for Fe:Te in the nominal range 1.04-1.18:1, while a report by Mizuguchi et al extended the phase diagram 15 up to 1.3:1.…”

Reversed anisotropy of the in-plane resistivity in the antiferromagnetic phase of iron tellurides

“…The phase diagram of Fe 1+x Te thus obtained and illustrated in Fig. 1(b) is consistent with the previous result obtained from the magnetic susceptibility measurements [19]. to the tetragonal-to-monoclinic structural transition accompanied by the paramagnetic-to-AFM transition.…”