Berlin 2012 – scientific programme
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KR: Fachgruppe Kristallographie
KR 2: Joint Session "Multiferroics I - Junctions and Thin Films / Magnetoelectric Coupling" (MA jointly with DF, DS, KR, TT), Organization: Manfred Fiebig (ETH Zürich)
KR 2.10: Talk
Monday, March 26, 2012, 12:15–12:30, EB 301
Multiferroicity and magnetoelectricity in a doped topological ferroelectric — Marco Scarrozza, Maria Barbara Maccioni, Giorgia M. Lopez, Alessio Filippetti, and •Vincenzo Fiorentini — Dept of Physics, U of Cagliari and CNR-IOM, Cagliari, Italy
La2Ti2O7 is a “topological” ferroelectric where dipoles are produced by antiferrodistortive rotations failing to compensate due to the layered structure. To turn on multiferroicity, we investigated magnetic doping from first-principles within density-functional theory. The isovalent substitution of Mn for Ti produces antiferromagnetism at all dopings as expected due to superexchange between Mn d3 ions. In the fully-substituted compound La2Mn2O7, many ordering patterns compete, the lowest being a variant of G-type antiferromagnetism. The same system is also magnetoelectric, because the rotations are involved in both magnetic and ferroelectric order: as a coercive field undoes the rotations and depolarizes ferroelectricity, magnetic coupling doubles in intensity. However, the ferromagnetic phase of La2Mn2O7 is always much higher in energy. On the other hand, we find that heterovalent substitution of Ti with Cr, Sc, and V always yields robust ferromagnetism. In particular, V orders in rows orthogonal to the P direction, with a covalency gap of 0.2 eV: La2Ti2−xVxO7 is therefore properly multiferroic. We are currently investigating the magnetoelectric tensors.