Muon spin rotation study of magnetism and superconductivity in Ba(Fe1-xCox)2As2 single crystals

Abstract

Using muon spin rotation (muSR) we investigated the magnetic and superconducting properties of a series of Ba(Fe1-xCox)2As2 single crystals with 0 =< x =< 0.15. Our study details how the antiferromagnetic order is suppressed upon Co substitution and how it coexists with superconductivity. In the non-superconducting samples at 0 < x < 0.04 the antiferromagnetic order parameter is only moderately suppressed. With the onset of superconductivity this suppression becomes faster and it is most rapid between x = 0.045 and 0.05. As was previously demonstrated by muSR at x = 0.055 [P. Marsik et al., Phys. Rev. Lett. 105, 57001 (2010)], the strongly weakened antiferromagnetic order is still a bulk phenomenon that competes with superconductivity. The comparison with neutron diffraction data suggests that the antiferromagnetic order remains commensurate whereas the amplitude exhibits a spatial variation that is likely caused by the randomly distributed Co atoms. A different kind of magnetic order that was also previously identified [C. Bernhard et al., New J. Phys. 11, 055050 (2009)] occurs at 0.055 < x < 0.075 where Tc approaches the maximum value. The magnetic order develops here only in parts of the sample volume and it seems to cooperate with superconductivity since its onset temperature coincides with Tc. Even in the strongly overdoped regime at x = 0.11, where the static magnetic order has disappeared, we find that the low energy spin fluctuations are anomalously enhanced below Tc. These findings point toward a drastic change in the relationship between the magnetic and superconducting orders from a competitive one in the strongly underdoped regime to a constructive one in near optimally and overdoped samples.

33 Pages, 9 Figures

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• Structural and magnetic phase transitions near optimal superconductivity in BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$
• Muon spin rotation and infrared spectroscopy study of magnetism and superconductivity in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$
• Doping evolution of antiferromagnetism and transport properties in the non-superconducting BaFe2-2xNixCrxAs2
• Magnetic field effects in electron systems with imperfect nesting
• Muon spin rotation and infrared spectroscopy study of $B{a}_{1-x}N{a}_{x}F{e}_{2}A{s}_2$
• A unified phase diagram of F-doped LaFeAsO by means of NMR and NQR parameters
• Competing superconducting and magnetic order parameters and field-induced magnetism in electron doped Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$
• Neutron spin resonance as a probe of superconducting gap anisotropy in partially detwinned electron underdoped NaFe${}_{0.985}$Co${}_{0.015}$As
• Crossover between magnetism and superconductivity in low H-doped LaFeAsO
• Magnetism and its coexistence with superconductivity in CaK(Fe${}_{0.949}$Ni${}_{0.051}$)${}_4$As${}_4$: muon spin rotation/relaxation studies
• Pressure-induced magnetism in iron-based superconductors $A$Fe${}_2$As${}_2$ ($A=$ K, Cs, Rb)
• Electronic inhomogeneities in the superconducting phase of CaFe1.96Ni0.04As2 single crystals