  Dielectric constant measurement under magnetic field is an efficient
technique to study the coupling between charges and spins in insulating
materials. For magnetic oxides, the geometric frustration is known to be a key
ingredient to observe such a coupling. Measurements for the triangular
Ising-like cobaltite Ca3Co2O6 have been made. Single crystals of Ca3Co2O6 are
found to exhibit a magnetodielectric effect below TN=25K with a peak in the
e(H) curve at the ferri to ferromagnetic transition. This relation between e
and magnetization has been modelized by using two order parameters in an energy
expansion derived from the Landau formalism and the fluctuation-dissipation
theorem. This result emphasizes the great potential of insulating transition
metal oxides for the search of magnetodielectric effect.
