Different response of the crystal structure to isoelectronic doping in BaFe2[As(1-x)P(x)]2 and [Ba(1-x)Sr(x)]Fe2As2

Abstract

Superconductivity up to 30 K in charge neutrally doped BaFe2[As(1-x)P(x)]2 has been ascribed to chemical pressure, caused by the shrinking unit cell. But the latter induces no superconductivity in [Ba(1-x)Sr(x)]Fe2As2 in spite of the same volume range. We show that the spin-density-wave (SDW) state of BaFe2As2 becomes suppressed in BaFe2[As(1-x)P(x)]2 by a subtle reorganization of the crystal structure, where arsenic and phosphorus are located at different coordinates z(As), z(P). High-resolution X-ray diffraction experiments with BaFe2[As(1-x)P(x)]2 single crystals reveal almost unchanged Fe-P bonds, but a contraction of the Fe-As bonds, which remain nearly unchanged in [Ba(1-x)Sr(x)]Fe2As2. Since the Fe-As bond length is a gauge for the magnetic moment, our results show why the SDW is suppressed by P-, but not by Sr-doping. Only the Fe-P interaction increases the width of the iron 3d bands, which destabilizes the magnetic SDW ground state. The simultaneous contraction of the Fe{As bonds is rather a consequence of the vanishing magnetism. Ordered structure models of BaFe2[As(1-x)P(x)]2 obtained by DFT calculations agree perfectly with the single-crystal X-ray structure determinations. The contraction of the Fe-As bonds saturates at doping levels above x = 0.3, which corrects the unreasonable linear decrease of the so-called pnictide height.

7 Pages, 8 Figures, citations added, text revised

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• Coincident structural and magnetic order in BaFe${}_2$(As${}_{1-x}$)P${}_x$)${}_2$ revealed by high-resolution neutron diffraction
• Disorder, critical currents, and vortex pinning energies in isovalently substituted BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$
• Spin excitations in optimally P-doped BaFe2(As0.7P0.3)2superconductor
• Anomalous phonon redshift in K-doped BaFe2As2 iron pnictides
• Origin of doping-induced suppression and reemergence of magnetism in LaFeAsO${}_{1-x}$H${}_x$
• Comprehensive study of out-of-plane transport properties in BaFe${}_2$As${}_2$: Three-dimensional electronic state and effect of chemical substitution
• Effects of 6 MeV proton irradiation on the vortex ensemble in BaFe${}_2$(As${}_{0.67}$P${}_{0.33}$)${}_2$ revealed through magnetization measurements and real-space vortex imaging
• Effects of Chemical Pressure on Superconductivity in Electrochemically Intercalated (TMA)yFe2(Se1-xSx)2 (TMA = Tetramethylammonium)
• Phase diagram of the isovalent phosphorous-substituted 122-type iron pnictides