Topological multiferroics

Based on first-principles calculations, we explore an unconventional type of multiferroicity obtained via magnetic doping of wide-gap layered-perovskite ferroelectrics of the family AnTinO3n+2. Using the n=4 member La2Ti2O7 as home base, we substitute 3d atoms for Ti. The highlights of our results are that (1) low-concentration substitution of Ti by V produces robust unidirectional ferromagnetic (FM) order, resulting in a small-gap proper multiferroic, which in addition has electrically switchable magnetization, and (2) the isovalent substitution of Mn for Ti produces multiferroicity with weak FM order due to canting of antiferromagnetic Mn spins, and larger-than-usual linear magnetoelectric coupling.