Berlin 2015 – scientific programme

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KR: Fachgruppe Kristallographie

KR 5: Multiferroics II (DF jointly with DS, KR, MA,TT)

KR 5.11: Talk

Wednesday, March 18, 2015, 18:05–18:20, EB 107

Tiny cause with large effects: the origin of the large magnetoelectric and magnetoelastic effect in EuTiO₃ — •Annette Bussmann-Holder — MPI-FKF, Heisenbergstr. 1, D-70569 Stuttgart, Germany

The magnetoelectric coupling in the perovskite EuTiO₃ is analyzed within a spin-phonon coupled Hamiltonian. It is shown that the tiny magnetostriction which accompanies the onset of antiferromagnetic order at T_N=5.7 K induces a substantial hardening in the soft optic mode and a drop in the dielectric constant. The reduction of magnetostriction with increasing magnetic field reverses this behavior. While for small fields ferromagnetic order rapidly sets in accompanied by a volume expansion, this is destroyed with increasing fields and a strange paramagnetic state obtained. This exotic observation can be understood as stemming from the interplay between the enhanced oxygen p Ti d dynamical covalency which alters the crystal field at the Eu site and inhibits the virtual transition from 4f7 to 4f65d responsible for ferromagnetic order.