Berlin 2015 – scientific programme
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MA: Fachverband Magnetismus
MA 22: Multiferroics I (DF with DS/KR/MA/TT)
MA 22.13: Talk
Wednesday, March 18, 2015, 12:45–13:00, EB 107
Ab Initio analysis of ferroelectric and magnetic properties of potentially multiferroic aurivillius phases — •Axiel Yael Birenbaum, Jan van den Broek, and Claude Ederer — Materials Theory, ETH Zürich
A promising class of high temperature polar magnetic multiferroic materials are the Aurivillius family of layered-perovskites related compounds. They combine high temperature ferroelectric properties with a layered structure that allows for systematic introduction of magnetic ions. The simplest of such cases to have been studied is Bi5FeTi3O15. However, no well-established value exists for its spontaneous electric polarization, and contradictory reports as to its magnetic states.
We perform Density Functional Theory calculations on Bi5FeTi3O15, and conclude on a high spontaneous electric polarization. To better understand the mechanism for ferroelectricity, we examine 9 systems, based on SrBi2Ta2O9 as reference. We find a high spontaneous polarization even in the case of with no nominally ferroelectrically-active cations. We discuss these results in light of the tri-linear coupling between soft and hard modes demonstrated for SrBi2Ta2O9 and the general concept of “hybrid improper ferroelectricity”. To clarify the range of temperatures expected for magnetic long range order despite a low concentration of magnetic ions and the short range of superexchange interactions, we perform Monte Carlo simulations. We discuss possible strategies to increase magnetic ordering temperatures.