Magnetic structure and spin dynamics of multiferroic system Co4Nb2O9

Co4Nb2O9, was recently reported to have large magneto-dielectric coupling effect under a certain magnetic field.[1,2] This compound has a corundum-type crystal structure of space group P-3c1 of ref. [3] and undergoes antiferromagnetic phase transition around 27 K. It was previously believed that the magnetic moments of Co2+ order into a collinear antiferromagnetic structure in which Co2+ spins order parallel to the c-direction and form ferromagnetic chains with antiparallel inter-chain coupling.[3] However, the recent study has shown that this magnetic structure model is incorrect.[4] In this study, we found that the Co2+ magnetic moments align in the ab plane with a non-collinear configuration. Using inelastic neutron scattering, we measured the spin wave excitation from its magnetic phase along (h00) and (00l). A magnetic model was proposed to explain the observed spin dynamical behavior. There are two inequivalent Co sites, which form spin chains in an alternative way along c axis. Each Co2+ moment couples with its two inequivalent neighbors on the same chain with ferromagnetic interactions. Co2+ moments from each site form a zig-zag hexagonal ring perpendicular to the c axis, where antiferromagnetic interactions dominate. On the basis of this model, the observed spin wave spectra can be well simulated by SpinW. [5]
Spin, Dynamics, Cobalt, Niobium, Coupling, Antiferromagnetic materials, Crystal structure, Inelastic scattering, Spin waves
Deng, G., Cao. Y., Ren, W., Cao, S., Gauthier, N., Kenzelmann, M., Studer, A., Rule, K., Gardner, J. S., Davison, G., Imperia, P., & McIntyre, G. J. (2017). Magnetic structure and spin dynamics of multiferroic system Co4Nb2O9. Paper presented to the 41st Annual Condensed Matter and Materials Meeting, Charles Sturt University, Wagga Wagga, NSW, Australia, 31st January - 3rd February 2017, (p.34). Retrieved from: