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Andreas Christoph Baum

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Room
E-Mail
Andreas.Baum@ph.tum.de
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Group
Technical Physics

Offered Bachelor’s or Master’s Theses Topics

Magnetokalorische Effekte in TmB4

The microscopic foundations of magnetism and related phenomena are very active fields in current research. This is especially true for peculiar configurations such as highly anisotropic materials or magnetic frustration, where the onset of order is suppressed due to the competition of different types of coupling. Rare-earth tetraborides are realizations of such systems. Recently a strong magnetocaloric effect was found in TmB4 [Orendáč et al., Sci. Rep. 8, 10933 (2018)] which indicates a strong relationship between magnetism and lattice. One can expect technical applications. It is the goal of this thesis to study the lattice excitations (phonons) in TmB4 using inelastic light (Raman) scattering in an applied magnetic field at the onset of the different phases. The work includes a thorough introduction to spectroscopy, low-temperature, and high-field techniques. Contact: Andreas Baum, Rudi Hackl

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Rudolf Hackl
Magnonen und Schalten von Spins in CuMnAs

Spin-based devices are considered very promising for fast and low-energy logics. This is especially true for antiferromagnets (AFM) which combine fast spin dynamics and resilience to external perturbation. The speed corresponds to the high energy of magnetic excitations (magnons), and the robustness to the vanishing net magnetization of an AFM. Recently the switching of magnetic states by external currents and the related changes in the transport properties were demonstrated for the AFM CuMnAs [Wadley et al., Science 351, 587 (2016)], making the compound a promising candidate for spintronic memory devices. On a more fundamental level, however, the spin dynamics in CuMnAs have not been studied so far. Inelastic light (Raman) scattering provides access to the dynamics of magnets [Devereaux and Hackl, Rev. Mod. Phys. 79, 175 (2007)] and one may obtain direct information on the relevant energies and spin dispersion.

It is planned to study CuMnAs in an applied magnetic field using Raman spectroscopy. The work includes an introduction to the physics of magnetism, spintronics, to spectroscopy, low-temperature, and high-field techniques.
Contact: Andreas Baum, Rudi Hackl, Mathias Weiler

suitable as
  • Bachelor’s Thesis Physics
Supervisor: Rudolf Hackl
Spin- und Gitter-Dynamik in EuFe2As2 Einkristallen

Iron-based pnictides and chalcogenides are model systems for complex materials having several electron bands, derived from Fe 3d orbitals, crossing the Fermi energy. These multiband systems are characterized by the proximity of various intertwined phases including unconventional superconductivity and magnetism. The magnetic state displays remarkable anisotropic properties which require mono-domain samples for successful studies. Mono-domain samples can be obtained by suppressing one of the two equivalent domain orientations, i.e. by de-twinning the crystals. Here, EuFe2As2 is unique since the twins may be removed in moderate magnetic fields. The samples stay single-domain even after switching off the field. This facilitates a “clean” experiment without the superposition of various fields. This study contributes to answer the question as to the driving force behind magnetism, structural distortions, and superconductivity in the iron-based compounds.

It is planned to study spin excitations and phonons in EuFe2As2 close to the various phase transition lines and to compare the spectroscopy results with theoretical predictions. The samples are prepared in the group of Philipp Gegenwart, University of Augsburg. For the related theory work there is a long-standing collaboration with groups in Frankfurt/Main (Roser Valentí) and Washington, D.C., USA (Igor Mazin).

The work includes a thorough introduction to spectroscopy, low-temperature, and high-field techniques. Contact: Andreas Baum, Rudi Hackl

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Rudolf Hackl
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