Synopsis: Magnetic order is no match for the lattice

Density-functional calculations provide a comprehensive picture of how magnetic order evolves with doping in two iron pnictide compounds.
Synopsis figure
Illustration: Alan Stonebraker

Understanding magnetic order in the two major families of iron-based superconductors with FeAs layers—namely, electron-doped LaFeAsO1-xFx and hole-doped Ba1-2yK2yFe2As2—is important because magnetism seems to be intimately tied with superconductivity. At about 150K, the undoped compounds (x and y = 0) acquire a ferromagnetic stripe ordering along the shorter axis of the square Fe sublattice, while displaying antiferromagnetic ordering along the longer axis and between the Fe layers. Doping with enough carriers suppresses the magnetic order and induces superconductivity in both compounds, though in Ba1-2yK2yFe2As2 magnetism and superconductivity coexist for 0.10<y<0.15.

Although density-functional calculations overestimate the value of the Fe moment, they generally reproduce the observed magnetic structure for undoped pnictides. In an article appearing in Physical Review B, Alexander Yaresko, Guo-Qiang Liu, Viktor Antonov, and Ole Krogh Andersen at the Max-Planck Institute in Stuttgart, Germany, present comprehensive calculations on experimentally observed crystal structures of LaFeAsO1-xFx and Ba1-2yK2yFe2As2 to determine the magnetic behavior as a function of doping. They find that electron doping above x>0.1 in LaFeAsO1-xFx destabilizes the stripe magnetic order and leads to an incommensurate spin spiral order, whereas hole-doping in Ba1-2yK2yFe2As2 leaves the magnetic stripe order intact up to y=0.25. The authors find that in both compounds, the classical Heisenberg model with nearest and next-nearest neighbor spin interactions is inadequate to describe the magnetic order and may require additional terms to accurately compute the energy. – Sarma Kancharla


More Features »


More Announcements »

Subject Areas


Previous Synopsis

Related Articles

Synopsis: The Signature of Magnetic Monopoles

Synopsis: The Signature of Magnetic Monopoles

Calcu­lations uncover the neutron-scattering signature of the magnetic monopoles that propagate through quantum spin ices. Read More »

Viewpoint: A Polka-Dot Pattern Emerges in Superfluid Helium

Viewpoint: A Polka-Dot Pattern Emerges in Superfluid Helium

A surprising two-dimensional pattern appears in superfluid helium-3 when the liquid is confined to a micrometer-thick cell and exposed to a magnetic field. Read More »

Synopsis: Putting a Spin on the Josephson Effect

Synopsis: Putting a Spin on the Josephson Effect

Researchers demonstrate spin splitting of localized electronic states, called Andreev bound states, in a superconducting device. Read More »

More Articles