Spin fluctuations and superconductivity in powders of Fe1+xTe0.7Se

Abstract

Using neutron inelastic scattering, we investigate the role of interstitial iron on the low-energy spin fluctuations in powder samples of Fe1+xTe0.7Se0.3. We demonstrate how combining the principle of detailed balance along with measurements at several temperatures allows us to subtract both temperature-independent and phonon backgrounds from S(Q, ω) to obtain purely magnetic scattering. For small values of interstitial iron (x = 0.009(3)), the sample is superconducting (Tc=14 K) and displays a spin gap of 7 meV peaked in momentum at wave vector q0=(π,π) consistent with single crystal results. On populating the interstitial iron sites, the superconducting volume fraction decreases and we observe a filling in of the low-energy magnetic fluctuations and a decrease of the characteristic wave vector of the magnetic fluctuations. For large concentrations of interstitial iron (x=0.048( 2)) where the superconducting volume fraction is minimal, we observe the presence of gapless spin fluctuations at a wavevector of q0=(π,0). We estimate the absolute total moment for the various samples and find that the amount of interstitial iron does not change the total magnetic spectral weight significantly, but rather has the effect of shifting the spectral weight in Q and energy. These results show that the superconducting and magnetic properties can be tuned by doping small amounts of iron and are suggestive that interstitial iron concentration is also a controlling dopant in the Fe1+xTe1−ySey phase diagram in addition to the Te/Se ratio.

Superconductivity and magnetism in 11-structure iron chalcogenides in relation to the iron pnictides

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“…Such complex magnetic systems have recently attracted renewed attention due to their potential route to colossal magnetoresistance [5] and multiferroic properties [6,7]. More recently, the importance of incommensurate magnetic spiral structures has been highlighted in the field of iron-based superconductors and related systems [8][9][10][11][12][13][14]. ZnCr 2 Se 4 displays both significant spin-phonon coupling [15] and magnetostriction [16], demonstrating the importance of fully understanding its structure and magnetism.…”

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