Violation of Superexchange Model in Multiferroic CoCr2O4

CoCr2O4 is a multiferroic with a proposed spin-current model dating from the 1960s. However, the model has not been verified due to the lack of data about the spin fluctuations. Our recent neutron spectroscopy experiments show that the exchange is highly frustrated and shows a novel coupling between commensurate and incommensurate spin waves. In order to solve the magnetic exchange parameters unambiguously, we propose to map the complete spin wave dispersion to help gain an understanding of the microscopic origin of ferroelectricity.