In-Plane Resistivity Anisotropy in the Magneto-Structurally Ordered Phase of Cu-Substituted Fe_1+xTe

Abstract

The in-plane resistivity anisotropy was studied using detwinned Fe 1+x-y Cu y Te single crystals.Sizable resistivity anisotropy was found in the magneto-structurally ordered phase, that is  a >  b , surprisingly opposite to that in iron pnictide. Our results also revealed an increase of resistivity anisotropy with the increasing concentration of impurity atoms-excess Fe and substituted Cu atoms, which suppressed the magnetic ordering. This is suggestive of the generic applicability of the recently proposed impurity-induced-anisotropy scenario for explaining the origin of resistivity anisotropy observed in Fe 1+x-y Cu y Te.

The influence of magnetic order on the magnetoresistance anisotropy of Fe1 + δ–xCuxTe

“…We showed in figure 3 that this effect is clearly decoupled from Lorentz force contributions to the magnetotransport and that it is only observable with a well defined current path along the in-plane crystal a/b axes. Resistance anisotropy has been observed previously in δ + Fe 1 Te [19,22,27,31] as well as selenium and copper substitutions thereof [19,27] detwinned by the application of uniaxial pressure. In the case of Fe 1.09 Te in situ x-ray measurements under uniaxial strain provided evidences for the resistance anisotropy being correlated to monoclinic domain population [31].…”

“…We notice that the magnitude of the resistance anisotropy is quite similar for = x 0 EDX and 0.04, but is much smaller for = x 0.05 EDX and 0.06 (see figure 6). Hence, a dominant extrinsic impurity effect of copper substitution on the magnitude of the resistance anisotropy as was suggested by some authors [19,27] seems unlikely. Instead our findings suggest an intrinsic origin of the resistance anisotropy.…”

“…However, ascribing a physical mechanism to the single-domain in-plane resistance anisotropy is complicated as such anisotropy can also arise from other intrinsic effects such as Hund's coupling between itinerant electron spins and local moments [22] or from extrinsic effects such as anisotropic impurity scattering [19,27]. Both Hund's coupling and anisotropic impurity scattering have been claimed to be significant in giving rise to the resistance anisotropy in δ + Fe 1 Te: the original study suggested both effects are needed to describe the evolution of the resistance anisotropy with annealing [22] while another group disputed this claiming that the resistance anisotropy is only due to impurity scattering [19,27]. In addition, an intrinsic mechanism based on the Fermi surface anisotropy has also been suggested to govern the resistance anisotropy in the electrondoped iron-pnictides [28].…”