Nuclear Magnetic Resonance in Multiferroic Ba2CoGe2O7
In the multiferroic compound Ba2CoGe2O7 the electric polarization is induced by the spin-dependent p-d-hybridization mechanism. As a result, the measured polarization is dependent on the orientation of the magnetic field H [1]. A detailed theoretical study concluded, that an additional antiferroelectric coupling term to the Hamiltonian is required to accurately explain the experimental findings [2].
Nuclear Magnetic Resonance (NMR) is a local probe, that allows access to the local magnetic fields as well as to the local electric field gradient (EFG) via the nuclear quadrupole moment. We obtained 59Co NMR spectra from the two inequivalent Cobalt sites Co(1) and Co(2) split by the electric quadrupole interaction, where the local magnetic fields at the two Co sites were found to modulate with a period of π/2. A periodical angular dependence of the EFG, which exhibits the same periodicity as the electric polarization Pc, was observed.
[1] H. Murakawa et al., Phys. Rev. Lett. 105, 137202 (2010)
[2] J. Romh´anyi et al., Phys. Rev. B 84, 224419 (2011)