Magnetoelectric emission in rare-earth doped ferroelectric crystals La2 Ti2 O7: R3+ (R=Er, Eu, and Nd)

The optical magnetoelectric (OME) effect, i.e., the change of optical response on the reversal of light propagation vector (k), has been investigated for the emission of rare earth R3+ ion (R=Nd, Eu, Er) doped in a ferroelectric La2 Ti2 O7 single crystal under magnetic field (H). The symmetry condition for the appearance of the OME effect for Hk was confirmed by varying the relative angle between the electric polarization and magnetic field. Another tensor component of the second-order magnetolectric tensor βijk for Hk, i.e., the magnetochiral effect, is allowed in the Faraday configuration but found to be small compared with the OME effect in the Voigt configuration. The importance of the spin-orbit coupling, the magnetic dipole transition, and the noncentrosymmetric crystal structure is discussed as the origin of the OME effect on the basis of the observed signal magnitude depending on the species of the rare-earth ion and its optical transition moment.