Magnetoelectric multiferroics

Magnetoelectric multiferroics are materials, which exhibit simultaneously magnetic and ferroelectric order. There is theoretically possible to influence magnetic or ferroelectric domains with electric or magnetic fields, respectively, therefore these materials are intensively studied for their promising potential applications in non-volatile memories. Unfortunately, there are only few multiferroics in nature and most of them work only at low temperatures. We suggested to use large mechanical strain in ultrathin films for preparation of new „artificial“ multiferroics. We proved that originally antiferromagnetic and paraelectric EuTiO₃ changes in films to strong ferromagnet and ferroelectrics due to strong spin-lattice coupling. Such system should exhibit strong magnetoelectric coupling which can be used in future memories. Paper was published in Nature [J. H. Lee et al., Nature 466, 954 (2010)].

We also suggested using strong internal electric field in multiferroic Eu_0.5Ba_0.5TiO₃ for the search of permanent electric dipole moment (EDM) of the electron. According to standard model of particles its value should be of order of 10^–40 e.cm. Recently it has been shown that spontaneous violation of charge parity symmetry is much larger then it follows from the standard model, therefore this model needs an extension. New particle theories propose EDM of electrons 8 or 12 orders of magnitude larger then the standard model. The physicists try to measure EDM of electron already 40 years, unfortunately fruitlessly. They reached sensitivity of only 10^–27 e.cm. We have shown that in multiferroic Eu_0.5Ba_0.5TiO₃ the sensitivity should be one order of magnitude higher. We synthesized this material and prepared ceramic samples suitable for this measurement. In case of successful determination of EDM value it will be possible to prove and specify new theories going beyond the standard model. The paper was published in Nature Materials [K. Z. Rushchanskii et al., Nature Mat. 9, 649 (2010)].

Fig. 1: Scheme of the principle of measurement of an electric dipole moment of the electron. Electric and magnetic moments of the electrons switch with switching of the electric field which leads to a change of the measured magnetization.