Observation of anomalous admixture of superconducting and magnetic fractions in BaFe2−xCoxAs2 single crystals

Increasing doping concentration (x) in pnictide superconductors leads to a loss of long range magnetic order and the emergence of superconductivity. In these doped compounds the role of magnetic fluctuations and their effect on superconductivity is not well understood. Below Tc, in optimally doped B...

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Bibliographic Details
Published in:New journal of physics 2016-06, Vol.18 (6), p.063025
Main Authors: Bag, Biplab, Vinod, K, Bharathi, A, Banerjee, S S
Format: Article
Language:English
Subjects:
Diamagnetism
Doping
doping effects
Group 5A compounds
Magnetic variations
Magnetism
Magnetization
Physics
pnictides
Single crystals
superconducting fluctuations
Superconductivity
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Summary:Increasing doping concentration (x) in pnictide superconductors leads to a loss of long range magnetic order and the emergence of superconductivity. In these doped compounds the role of magnetic fluctuations and their effect on superconductivity is not well understood. Below Tc, in optimally doped BaFe2−xCoxAs2 single crystals at low applied magnetic fields (H), we observe a coexistence of regions with both positive and negative (diamagnetic) magnetization response. With increasing H the positive magnetization response weakens and the diamagnetic signal associated with superconductivity enhances. Above Tc, resistivity and magnetization measurements in the normal state of the material reveals the presence of a weak diamagnetic response admixed with the magnetic response of a magnetized state. Magneto-optical imaging studies in the optimally doped sample shows a spatially inhomogeneous local magnetic response in the normal state with local regions having diamagnetic like response existing alongside magnetized regions with short range magnetic order. Above Tc, the estimated volume fraction with diamagnetic fluctuations is found to be maximum in the optimally doped sample. We present a doping dependent H-T diagram identifying different fluctuation regimes. We propose our results suggest the admixture of magnetic and superconducting fractions in BaFe2−xCoxAs2 and a close correlation between them.
ISSN:1367-2630
DOI:10.1088/1367-2630/18/6/063025