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Tuesday, 09 December 2014

Dr. Nicholas Bristowe presented his research on novel multiferroics in an ICN2 Seminar

Dr. Nicholas Bristowe has got a strong background in perovskyte materials and is now Research Fellow at the Department of Materials of the Imperial College London (UK). He was introduced by Dr. José Miguel Alonso Pruneda before exploring improper ferroelectricity in two different perovskite superlattice systems using first principles calculations and a symmetry mode analysis.

After a fruitful collaboration with the ICN2 Theory and Simulation Group, Dr. Nicholas Bristowe offered today an ICN2 Seminar entitled “Exploiting lattice mode couplings to design novel multiferroics”. He has got a strong background in perovskyte materials and is now Research Fellow at the Department of Materials of the Imperial College London (UK). His main research focus is the fundamental understanding of oxide ceramics and their interfaces from first-principles quantum mechanical calculations. The speaker was introduced by Dr. José Miguel Alonso Pruneda.

The possibility of tuning the magnetic properties of a material with an applied electric field has received particular attention within the field of perovskites for novel magnetoelectric memory devices. In this regard, a promising route to achieve the elusive ferroelectric (anti)ferromagnet is by exploiting the so-called rotationally driven improper ferroelectricity. Here the polarisation is no longer the primary order parameter, but instead one or more antiferrodistortive (AFD) motions, corresponding to rotations of the oxygen octahedra, drives the polarisation. These AFD motions, unlike ferroelectricity, are ubiquitous in magnetic perovskites.

During the ICN2 Seminar held today the speaker explored improper ferroelectricity in two different perovskite superlattice systems using first principles calculations and a symmetry mode analysis. In the first, consisting of halfdoped layered titanates, the AFD motions are found to not only induce a ferroelectric polarisation approaching that of the prototypical BaTiO3, but are also found to be key for favouring an unexpected ferromagnetic ground state. In the second superlattice made up of vanadates, hi research revealed a Jahn-Teller motion induced ferroelectricity.

The possibility for an electric field control of Jahn-Teller motions, instead of AFD, may enable a new paradigm for creating efficient magetoelectrics and a functional control of electronic properties more generally.