Competing magnetic ground states in nonsuperconducting Ba(Fe1−xCrx)2As2as seen via neutron diffraction (original) (raw)
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Neutron scattering study of the interplay between structure and magnetism inBa(Fe1−xCox)2As2
Physical Review B, 2009
Single crystal neutron diffraction is used to investigate the magnetic and structural phase diagram of the electron doped superconductor Ba(Fe1−xCox)2As2. Heat capacity and resistivity measurements have demonstrated that Co doping this system splits the combined antiferromagnetic and structural transition present in BaFe2As2 into two distinct transitions. For x=0.025, we find that the upper transition is between the high-temperature tetragonal and low-temperature orthorhombic structures with (TTO = 99 ± 0.5 K) and the antiferromagnetic transition occurs at TAF = 93 ± 0.5 K. We find that doping rapidly suppresses the antiferromagnetism, with antiferromagnetic order disappearing at x ≈ 0.055. However, there is a region of coexistence of antiferromagnetism and superconductivity. The effect of the antiferromagnetic transition can be seen in the temperature dependence of the structural Bragg peaks from both neutron scattering and x-ray diffraction. We infer from this that there is strong coupling between the antiferromagnetism and the crystal lattice.
Hole-doped BaFe2-xCrxAs2 Crystals: A Case of Non-superconductivity
We investigate the physical properties and electronic structure upon Cr-doping in the iron arsenide layers of BaFe 2 As 2 . This form of hole-doping leads to suppression of the magnetic/structural phase transition in BaFe 2-x Cr x As 2 for x > 0, but does not lead to superconductivity. For various x values, temperature dependence of the resistivity, specific heat, magnetic susceptibility, Hall coefficient, and single crystal x-ray diffraction data are presented. The materials show signatures of approaching a ferromagnetic state with x, including a metamagnetic transition for x as little as 0.36, an enhanced magnetic susceptibility, and a large Sommerfeld coefficient. Such results reflect renormalization due to spin fluctuations and they are supported by density functional calculations at x = 1.
Muon spin rotation study of magnetism and superconductivity in Ba(Fe1−xCox)2As2single crystals
Physical Review B, 2012
Using muon spin rotation (µSR) we investigated the magnetic and superconducting properties of a series of Ba(Fe 1-x Co x) 2 As 2 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 µSR at x = 0.055 [P.
Journal of the Physical Society of Japan, 2009
We report a systematic investigation of Ba(Fe 1Àx Co x) 2 As 2 based on transport and 75 As NMR measurements, and establish the electronic phase diagram. We demonstrate that doping progressively suppresses the uniform spin susceptibility and low frequency spin fluctuations. The optimum superconducting phase emerges at x c ' 0:08 when the tendency toward spin ordering completely diminishes. Our findings point toward the presence of a quantum critical point near x c between the SDW (spin density wave) and superconducting phases.
2008
The recent discovery and subsequent developments of FeAs-based superconductors have presented novel challenges and opportunities in the quest for superconducting mechanisms in correlated-electron systems. Central issues of ongoing studies include interplay between superconductivity and magnetism as well as the nature of the pairing symmetry reflected in the superconducting energy gap. In the cuprate and RE(O,F)FeAs (RE = rare earth) systems, the superconducting phase appears without being accompanied by static magnetic order, except for narrow phase-separated regions at the border of phase boundaries. By muon spin relaxation measurements on single crystal specimens, here we show that superconductivity in the AFe_2As_2 (A = Ca,Ba,Sr) systems, in both the cases of composition and pressure tunings, coexists with a strong static magnetic order in a partial volume fraction. The superfluid response from the remaining paramagnetic volume fraction of (Ba_0.5K_0.5)Fe_2As_2 exhibits a nearly ...
Doping – Dependent irreversible magnetic properties of Ba(Fe1−xCox)2As2 single crystals
Physica C: Superconductivity, 2009
We discuss the irreversible magnetic properties of self-flux grown Ba(Fe 1-x Co x ) 2 As 2 single crystals for a wide range of concentrations covering the whole phase diagram from the underdoped to the overdoped regime, x=0.038, 0.047, 0.058, 0.071, 0.074, 0.10, 0.106 and 0.118. Samples were characterized by a magneto-optical method and show excellent spatial uniformity of the superconducting state down to at least the micrometer scale. The in-plane properties are isotropic, as expected for the tetragonal symmetry, and the overall behavior closely follows classical Bean model of the critical state. The field-dependent magnetization exhibits second peak at a temperature and dopingdependent magnetic field, ( ) , p H T x . The evolution of this fishtail feature with doping is discussed. In particular we find that p H , measured at the same reduced temperature for different x, is a unique monotonic function of the superconducting transition temperature, ( ) c T x , across all dopings. Magnetic relaxation is time-logarithmic and unusually fast. Similar to cuprates, there is an apparent crossover from collective elastic to plastic flux creep above p H . At high fields, the field dependence of the relaxation rate becomes doping independent. We discuss our results in the framework of the weak collective pinning and show that vortex physics in iron-based pnictide crystals is much closer to highc T cuprates than to conventional s-wave (including MgB 2 ) superconductors.
Competitive and cooperative electronic states in Ba(Fe1−xTx)2As2 with T = Co, Ni, Cr
npj Quantum Materials, 2021
The electronic inhomogeneities in Co, Ni, and Cr doped BaFe2As2 single crystals are compared within three bulk property regions: a pure superconducting (SC) dome region, a coexisting SC and antiferromagnetic (AFM) region, and a non-SC region. Machine learning is utilized to categorize the inhomogeneous electronic states: in-gap, L-shape, and S-shape states. Although the relative percentages of the states vary in the three samples, the total volume fraction of the three electronic states is quite similar. This is coincident with the number of electrons (Ni0.04 and Co0.08) and holes (Cr0.04) doped into the compounds. The in-gap state is confirmed as a magnetic impurity state from the Co or Ni dopants, the L-shape state is identified as a spin density wave which competes with the SC phase, and the S-shape state is found to be another form of magnetic order which constructively cooperates with the SC phase, rather than competing with it.
Superconducting properties in heavily overdoped Ba(Fe0.86Co0.14)2As2 single crystals
Solid State Communications, 2015
In this work we report the influence of intrinsic superconducting parameters on the vortex dynamics in an overdoped Ba(Fe 1-x Co x) 2 As 2 (x=0.14) single crystal. We find a superconducting critical temperature of 13.5 K, magnetic penetration depth λ ab (0) = 660 ± 50 nm, coherence length ξ ab (0) = 5 nm, and the upper critical field anisotropy γ T→Tc ≈ 3.7. In fact, the Ginzburg-Landau model may explain the angular dependent H c2 for this anisotropic three-dimensional superconductor. The vortex phase diagram, in comparison with the optimally doped compound, presents a narrow collective creep regime. In addition, we found no sign of correlated pinning along the c axis. Our results show that vortex core to defect size ratio and λ play an important role in the resulting vortex dynamics in materials with similar intrinsic thermal fluctuations.