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PhD ceremony Mr. A.M.T. Pradipto: Local interactions in magnetic and ferroelectric materials: magnetic and vibronic couplings

When:Fr 07-06-2013 at 16:15

PhD ceremony: Mr. A.M.T. Pradipto, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Local interactions in magnetic and ferroelectric materials: magnetic and vibronic couplings

Promotor(s): prof. R. Broer, prof. C. de Graaf

Faculty: Mathematics and Natural Sciences

Many materials containing transition metal (TM) ions exhibit fascinating phenomena which may lead to important technological applications. Among the most important properties are those arising from magnetic interactions, often present in compounds containing TM ions with partially filled d-shells.The magnetic properties are governed by how the unpaired spins, mainly localized on the metal ions, interact with each other.

Their isotropic interactions lead to the parallel alignments or antiparallel alignments of the spins, these are the so-called ferromagnetic and antiferromagnetic interactions, respectively. Due to relativistic effects like the spin-orbit coupling, the spin moments can also interact anisotropically.

The discovery of ferroelectricity in materials with spiral-magnetic ordering added an important aspect of magnetic anisotropy in materials, in particular of the Dzyaloshinskii-Moriya interactions. Despite its importance, the study of magnetic anisotropy has been rather limited compared to the isotropic counterparts, and this is in part related to the difficulties in the extraction procedures of the anisotropic interaction parameters. We discuss in this thesis the methods to compute the anisotropic interactions, in addition to the isotropic ones, with applications to the CuO and LiCu2O2 multiferroic materials. This topic constitutes the major part of the thesis. In addition, we also investigate two models that describe the ferroelectric instability; the soft-mode and vibronic interaction models. We discuss these two mechanisms and illustrate our results for the prototype proper ferroelectric material, BaTiO3.

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