SNS Shows Novel Spin Waves in Iron Chalcogenide Fe1.05Te

January 2, 2011

^{Magnetic structure of the (a) iron chalcogenide, and (b) iron pnictide systems, showing exchange couplings of the Heisenburg Hamiltonian.}

Measurements conducted at the Spallation Neutron Source at ORNL have determined exchange couplings in the mag- netically ordered chalcogenide Fe_1.05Te, a nonsuperconducting member of the iron-based family of superconductors. The results show the exchange pairings thought to be related to superconductivity occur in a next-nearest-neighbor ordering of atoms, rather than in nearest-neighbor order as in a previously studied iron arsenide.

Researchers from the University of Tennessee, ORNL, and other institutions collaborated to study the spin waves in Fe_1.05Te. Superconductivity in iron-based superconductors emerges in proximity to magnetic order; similarly, many researchers think superconductivity in the copper oxides is driven by magnetic fluctuations. The magnetic order in Fe_1.05Te is considerably different from the related iron pnictide superconducting system, raising the question of whether magnetism can in both cases still drive the superconductivity in iron-based superconductors.

To answer that question, the exchange coupling energies in the Fe_1.05Te system were charac- terized using the ARCS instrument at SNS and other instruments to measure the spin waves and fitting the waves to a Heisenburg Hamiltonian. The dispersion of the spin waves in this sys- tem is novel and very different from that in the previously measured iron pnictide CaFe2As2. Fitted exchange couplings of J_1a =-17.5 ± 5.7, J_1b = -51.0 ± 3.4, J₂ = J_2a ≈ J_2b = 21.7 ± 3.5, J₃ = 6.8 ± 2.8 meV were found.

The University of Tennessee, Knoxville

Shull Wollan Center

SNS Shows Novel Spin Waves in Iron Chalcogenide Fe1.05Te