Superconductivity in pnictide materials
13 Aug 2009




ARGUS has been used to probe the magnetic fluctuations and phase diagram of a novel series of pnictide superconductors.


ARGUS is a general purpose muon spectrometer used across a broad range of scientific areas. These include magnetism, superconductivity, semiconductors, polymer dynamics, and muonic radical chemistry.

Some recent highlights from the ARGUS experimental programme are described below:

Superconductivity and magnetism coexist in the series of pnictide superconductors SmFeAsO1-xFx

AJ Drew (Queen Mary, University of London) and collaborators

Contact: Dr AJ Drew,

Further reading: AJ Drew et al., Phys. Rev. Lett. 101 (2008) 097010;

AJ Drew et al., Nature Materials 8 (2009) 310

The series of pnictide superconductors SmFeAsO1-xFx rapidly came to attention in early 2008 as the Tc value was among the highest found in this type of material. Two sets of experiments done using muon instruments at ISIS provided early and important information on this series of compounds.

Measurements on heavily fluorine doped specimens with x=0.18 and 0.3 showed that there was an unusual enhancement of magnetic spin fluctuations in the vicinity of the superconducting transition, due to the crystal field levels of the samarium ions present in these materials.

Subsequent measurements at ISIS (in combination with work done at the Paul Scherrer Institute) allowed the magnetic and superconducting phase diagrams of this series of materials to be mapped out in detail. This showed that there was a narrow intermediate doping region where superconductivity and ordered iron magnetism occurs through the bulk of the samples. This is different from other series of iron arsenide superconductors and draws an important parallel with the behaviour of cuprate superconductors, where coexisting magnetism and superconductivity have also been confirmed using muons. 

Phase diagram of Sm1111

The phase diagram of the Sm1111 iron arsenide superconductor has been determined using muon spin rotation and bulk techniques. The results show a coexistence between static magnetism and superconductivity.
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