Competing exchange interactions on the verge of a metal-insulator transition in the two-dimensional spiral magnet Sr3Fe2O7

We report a neutron scattering study of the magnetic order and dynamics of the bilayer perovskite Sr 3 Fe 2 O 7 , which exhibits a temperature-driven metal-insulator transition at 340 K. We show that the Fe 4+ moments adopt incommensurate spiral order below T N =115 K and provide a comprehensive description of the corresponding spin-wave excitations. The observed magnetic order and excitation spectra can be well understood in terms of an effective spin Hamiltonian with interactions ranging up to third-nearest-neighbor pairs. The results indicate that the helical magnetism in Sr 3 Fe 2 O 7 results from competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions whose strengths become comparable near the metal-insulator transition. They thus confirm a decades-old theoretical prediction and provide a firm experimental basis for models of magnetic correlations in strongly correlated metals. © 2014, American Physical Society.

Keywords

Neutrons, Magnetism, Hamiltonians, Ferromagnetism, Metals, Experiment planning

Citation

Kim, J. H., Jain, A., Reehuis, M. , Khaliullin, G., Peets, C., Ulrich, J. T., part, J. T., Faulhaber, E., Hoser, A., Walker, H. C., Adroja, D. T., Walters, A. C., Onosov, D. S., Maljul, A., & Keimer, B (2014). Competing exchange interactions on the verge of a metal-insulator transition in the two-dimensional spiral magnet Sr3Fe2O7. Physical Review Letters, 113(14), 147206. doi:10.1103/PhysRevLett.113.147206