Magnetic order tuned by Cu substitution in Fe1.1−zCuzTe

Abstract

We study the effects of Cu substitution in Fe1.1Te, the non-superconducting parent compound of the iron-based superconductor, Fe1+yTe1−xSex, utilizing neutron scattering techniques. It is found that the structural and magnetic transitions, which occur at ∼ 60 K without Cu, are monotonically depressed with increasing Cu content. By 10% Cu for Fe, the structural transition is hardly detectable, and the system becomes a spin glass below 22 K, with a slightly incommensurate ordering wave vector of (0.5-δ, 0, 0.5) with δ being the incommensurability of 0.02, and correlation length of 12Å along the a axis and 9Å along the c axis. With 4% Cu, both transition temperatures are at 41 K, though short-range incommensurate order at (0.42, 0, 0.5) is present at 60 K. With further cooling, the incommensurability decreases linearly with temperature down to 37 K, below which there is a first order transition to a long-range almost-commensurate antiferromagnetic structure. A spin anisotropy gap of 4.5 meV is also observed in this compound. Our results show that the weakly magnetic Cu has large effects on the magnetic correlations; it is suggested that this is caused by the frustration of the exchange interactions between the coupled Fe spins.

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

“…The cuts prove the result reported previously that the propagation vector is q 0 = 0.46 ± 0.01 and is incommensurate with respect to the nuclear positions. This contrasts with some studies that have stated that the propagation vector is taken as (0.5 − δ,0,0.5) [44] and is only clear in the current data set given the broad momentum coverage afforded by the WAND diffractometer. Figure 10 illustrates an extensive reciprocal-space map at 4 K (in the magnetically ordered state) and also at high temperatures of 80 K, where Fe 1.124 (5) Te is paramagnetic.…”

“…More correlated, in momentum, incommensurate scattering at (0.46, 0, 0.5) was reported in superconducting samples of Fe 1.02 Te 0.75 Se 0.25 [43]. Studies of Fe 1−z Cu z Te observe that this short-range incommensurate order at (∼0.42, 0, 0.5) seems to be stabilized with copper doping [44]. All of these studies illustrate that short-range incommensurate order at (∼0.45, 0, 0.5) competes and even coexists with superconductivity and also the two distinct collinear and helical magnetic phases described above in the absence of anion doping.…”

In-Plane Resistivity Anisotropy in the Magneto-Structurally Ordered Phase of Cu-Substituted Fe1+xTe

“…Upon Cu substitution, T s is reduced systematically from T s = 69 K for Cu-free samples to T s = 44 K for 3% Cu-substituted samples. This observation suggests that Cu atoms effectively substitute for in-plane Fe, causing a reduction in ordering probably due to magnetic frustration of a Cu ion with smaller magnetic moment [19]. Contrary to the strong scattering effect of excess Fe on the absolute value of resistivity, upon Cu substitution resistivity shows little change in the metallic region of resistivity below T s .…”

ChemInform Abstract: Magnetic Neutron Scattering Studies on the Fe‐Based Superconductor System Fe1+yTe1‐xSex

“…In the latter sample, the structural phase transition is not obvious and a transition to a spin-glass state is found at 22 K [209]. In Fe 1.06 Cu 0.04 Te, the initial structural and magnetic ordering occurs at 41 K, involving short-range incommensurate order that abruptly shifts to long-range nearly-commensurate order below 36 K [209]. Inelastic scattering measurements indicate a spin anisotropy gap of 4.5 meV in the nearly-commensurate phase [209].…”

“…In Fe 1.06 Cu 0.04 Te, the initial structural and magnetic ordering occurs at 41 K, involving short-range incommensurate order that abruptly shifts to long-range nearly-commensurate order below 36 K [209]. Inelastic scattering measurements indicate a spin anisotropy gap of 4.5 meV in the nearly-commensurate phase [209]. The results are consistent with the idea that the frustration of the exchange interactions between the coupled Fe spins increases as more Cu is added.…”