Magnetoelectric emission in rare-earth doped ferroelectric crystalsLa2Ti2O7: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 $(\mathbit{k})$, has been investigated for the emission of rare earth ${R}^{3+}$ ion ($R=\text{Nd}$, Eu, Er) doped in a ferroelectric ${\text{La}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$ single crystal under magnetic field $(\mathbit{H})$. The symmetry condition for the appearance of the OME effect for $\mathbit{H}\ensuremath{\perp}\mathbit{k}$ was confirmed by varying the relative angle between the electric polarization and magnetic field. Another tensor component of the second-order magnetolectric tensor ${\ensuremath{\beta}}_{ijk}$ for $\mathbit{H}\ensuremath{\parallel}\mathbit{k}$, 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.