We showed recently that V-doped La2Ti2O7 is properly multiferroic [1]. Ferromagnetism is driven by the ordering of V into dimerized chains along the a crystal axis, whereas polarization is due to composite, mainly rotational modes (around the same axis) whose net dipoles along the c crystal axis fail to compensate due to the layered structure. In [1] we estimated that the vibrational magnetoelectric response around the equilibrium structure due to the subset of modes inducing ferroelectricity should be marginal.
Here instead we directly explore magnetoelectric coupling upon complete polarization reversal between the two equivalent equilibrium states, a reversal which is easily obtained by a DC field. Using ab-initio magnetic-anisotropy calculations, we find that V spins point approximately along the b crystal axis in one polarization state, whereas they reverse to -b in the other state (with a substantial ~1 meV b/-b anisotropy energy). The spins seem to reorient by rotating through the a direction, which is the hard axis at equilibrium. In summary, polarization switching is accompanied by magnetization switching, and therefore the magnetization M can indeed be switched electrically.
We note in passing that while LTO has P=(0,0,Pc), upon V doping polarization acquires a component along a, i.e. P=(PV,0,Pc). As the polarization Pc c is reversed (e.g. by an electric field E0c, and M=MVb is reversed with it, as we showed), the component Pv a remains unchanged, i.e. the polarization is not inverted but rather reflected through the a-b plane. We suspect, and are investigating, a relation of this finding with magnetization inversion
