Master Thesis

PUBDB-2022-01378

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Investigation of the magnetic and electronic properties of topological insulator/ferromagnet heterostructures

Marotzke, S. (Corresponding author)DESY* ; Gruebel, G. (Thesis advisor)XFEL.EU*DESY* ; Rossnagel, K. (Thesis advisor)DESY*

2022

Abstract: In recent years, the application of topological principles in physics has paved the way for the discovery of a wide range of topological materials with potential applications in spintronics, zero-resistance materials and quantum computing. Hereby, heterostructures with topological insulators (TIs) as one component and a magnetic material as another play an important role as new topological phases have been predicted in these systems. One idea is that a topological phase transition could be realized by manipulating the magnetic state. To this aim, a precise understanding of the magnetic and electronic properties of such heterostructures is required.In this thesis, topological insulator/ferromagnet heterostructures consisting of the topological insulator Bi$_2$Se$_3$ and a ferromagnetic overlayer X/Co/Pt, with X = None, Pt, B$_4$C and B$_4$C/Pt, are investigated. The magnetic characterization via the magneto-optical Kerr effect reveal that the magnetic properties of the overlayer can be set by varying the sample design as well as the thickness of the individual layers. Particularly, overlayers that either exhibit perpendicular magnetic anisotropy with full or no remanence are identified. In the measurements of the electronic properties of the heterostructures via X-ray photoemission spectroscopy, two Bi phases are identified. By systematically varying the photon energy, the depth, in which the two Bi phases are located in the heterostructures, is analyzed. Possible reasons for the existence of two Bi phases as well as suggestions for necessary future investigations in order to expand the knowledge on the electronic and structural properties of the heterostructures are discussed. Finally, a scheme to invert the heterostructures is presented and tested via X-ray photoemission spectroscopy. This scheme has the potential of achieving momentum resolution in angle-resolved photoemission spectroscopy measurements of topological insulators in proximity to a ferromagnetic layer. Thus, the influence of the manipulation of the magnetization in the overlayer on the topological insulator could be investigated in future, possibly realizing a magnetic switch for a topological phase transition.

Note: Masterarbeit, University of Hamburg, 2021

---

Contributing Institute(s):

1. FS-FLASH (CFEL-UDSS)
2. Coherent X-ray Scattering (FS-CXS)
3. FS-SXQM (FS-SXQM)

Research Program(s):

1. 632 - Materials – Quantum, Complex and Functional Materials (POF4-632) (POF4-632)
2. 6G3 - PETRA III (DESY) (POF4-6G3) (POF4-6G3)
3. FS-Proposal: I-20200269 (I-20200269) (I-20200269)
4. FS-Proposal: I-20210224 (I-20210224) (I-20210224)

Experiment(s):

1. PETRA Beamline P04 (PETRA III)

Appears in the scientific report 2022

---