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B8: Stress and lattice dynamics of multiferroic systems

Our project elucidates the interplay between surface stress, interface stress and lattice dynamics of atomic layers near the surface region of oxidic and ferroic systems. Previously, we have studied the coupling between ferroelectric and magnetic effects, as conveyed by elasticity and by the spin-dependent electronic structure. This previous work has provided worldwide the first quantitative data on i) mechanical stress in barium titanate (BTO) and strontium titanate (STO) atomic layers on a variety of different single crystal substrates, ii) identification of BTO surface phonons and their dependence of layer thickness and lattice strain, iii) complete dispersion relation of surface phonons in epitaxial oxide films in combination with iv) a comprehensive quantitative atomic structure analysis.

In the new funding period we plan to extend our studies to the recently discovered quasicrystalline interfaces and their approximants in BTO on Pt(111). We focus on small energy excitations of the crystalline and of the quasicrystalline phase. Our work will provide first insights into the interplay between lattice dynamics, stress, and structure in quasicrystalline systems. Stress measurements are performed to investigate in situ the postulated effect of interfacial structural frustration on the formation of interface-driven quasicrystals. The quasicrystalline phase will be used as a template for the subsequent growth of ferromagnetic atomic layers on top. Thus, we characterize for the first time structural and magnetic properties of quasicrystalline multiferroic composites. Furthermore, we continue combined phonon spectroscopy and stress measurements of ultrathin oxide films on ternary systems of potential ferroic character to advance the understanding of the corresponding coupling mechanisms.

Principal Investigators

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