Structure, magnetic order and superconductivity in FeAs compounds – Niels Bohr Institute - University of Copenhagen

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Niels Bohr Institute > Calendar > 2009 > Structure, magnetic or...

Structure, magnetic order and superconductivity in FeAs compounds

Talk by Dimitri Argyriou
Much excitement has surrounded the discovery of superconductivity in Fe-pnictide. With the first report of superconductivity in the LaFeAsO the range and structural families of superconducting pnictide compounds has rapidly expanded with maximum reported Tc of about 50K.

In this talk I shall describe our recent neutron scattering work on the parent compounds in two pnictide superconducting families, PrFeAsO and MFe2As2 (M=Ca and Ba). We find that on cooling these materials magnetic ordering is associated with a transition from a tetragonal to orthorhombic symmetry.

For the CaFe2As2 both the magnetic and structural transitions are first order, while for the PrFeAsO the magnetic ordering of Fe appears a few kelvin below the structural transition. Our measurements under pressure have revealed that CaFe2As2 undergoes a first order transition to a tetragonal phase with a 5% volume collapsed.

This collapsed phase is non-magnetic confirmed by the absence of magnetic reflections measured by neutron diffraction.