1203.6181 (P. Toulemonde et al.)

Dependance of the structural and physical properties of
Tl1-yFe2-z(Se1-xSx)2 with isovalent substitution of Se by S: decrease of
TNeel with S content    [PDF]

P. Toulemonde, D. Santos-Cottin, Ch. Lepoittevin, P. Strobel, J. Marcus

The effect of selenium substitution by sulfur or tellurium in the Tl1-yFe2-zSe2 antiferromagnet was studied by x-ray and electron diffraction, magnetization and transport measurements. The full solid solution series Tl1-yFe2-z(Se1-xXx)2 was synthesized for X=Se and up to x=0.5 for X=Te, using the sealed tube technique. No superconductivity was found down to 4.2K in the case of sulfur despite that the optimal crystallographic parameters, determined by Rietveld refinements, are reached in the series (i.e. the Fe-(Se,S) interplane height and (Se,S)-Fe-(Se,S) angle for which the critical superconducting transition Tc is usually maximal in pnictides). Compounds substituted with tellurium, at least up to x=0.25, show superconducting transitions but probably due to tetragonal Fe(Se,Te) impurity phase. Transmission electron microscopy confirmed the existence of ordered iron vacancies network in S-substituted samples (in tetragonal sqrt(5) a \times sqrt(5) a \times c superstructure (I4/m) or in orthorhombic sqrt(2) a \times2sqrt(2) a \times c supercell (Ibam)). The Neel temperature (TN) indicating the onset of antiferromagnetism order decreases from 450K in the selenide (x=0) to 330K in the sulfide (x=1). We finally demonstrate a direct linear relationship between TNeel and the Fe-(Se,S) bond length (or Fe-(Se,S) height).

View original: http://arxiv.org/abs/1203.6181