Asymmetrically sandwiched ferromagnetic thin films display a large number of spin-orbit effects, including the Dzyaloschinsii-Moriya interaction (DMI), spin-orbit torques (SOT) and magnetoresistance (MR) effects. Their concurrence promises the implementation of interesting magnetic structures like skyrmions in future memory and logic devices. The complex interplay of various effects originating from the spin-orbit coupling and their dependencies on the microstructural details of the material system mandates a holistic characterization of its properties. In this PhD thesis, a comprehensive study of the spin-orbit effects in a chromium oxide/cobalt/platinum trilayer sample series is presented. The determination of the complete micromagnetic parameter set is based on a developed measurement routine that utilizes quasistatic methods. The unambiguous quantification of all relevant constants is crucial for the modeling of the details of magnetic structures in the system. In this context the necessity of a strict distinction of magnetic objects, that are stabilized by magnetostatics or the DMI, was revealed. Furthermore, a sample layout was developed to allow for the simultaneous quantification of the magnitudes of SOTs and MR effects from nonlinear magnetotransport measurements. In conjunction with a structural characterization, the dominating dependence of the effect magnitudes on microstructural details of the systems is concluded. Precisely characterized systems establish a solid groundwork for further investigations that are needed for viable skyrmion-based devices.:1 Introduction
2 Fundamentals
2.1 Towards new devices
2.2 Spin-orbit effects
2.2.1 Spin-current sources
2.2.2 Magnetoresistanceeffects
2.2.3 Spin-orbit torques
2.2.4 Harmonic analysis
2.3 Micromagnetic model
2.3.1 Dzyaloshinskii-Moriya interaction (DMI)
2.3.2 Consequences of the DMI for magnetic structures
2.3.3 Interface-induced DMI in asymmetrically stacked ferromagnets
2.3.4 Quantification of the interface-induced DMI
2.3.5 Levy-Fert three-site model including roughness
3 The CrOx/Co/Pt sample system
3.1 Experimental techniques
3.2 Structural characterization
4 Complete micromagnetic characterization
4.1 Magnetometry
4.1.1 Static investigation
4.1.2 Ferromagnetic resonance
4.2 DMI quantification
4.2.1 Field-driven domain wall creep motion
4.2.2 Asymmetric domain growth
4.2.3 Winding pair stability
4.3 Determination of the exchange parameter
4.3.1 Generation of circular magnetic objects
4.3.2 Homochiral magnetic bubble domains
4.4 Results
5 Magnetotransport measurements
5.1 Measurement setup
5.2 Magnetoresistance effects
5.3 Spin-orbit torque quantification
5.4 Results
6 Discussion
6.1 Structural predomination of the DMI strength
6.2 Ultra-thin limit exchange parameter reduction
6.3 Magnetotransport properties
6.4 Magneticstructures in //CrOx/Co/Pttrilayers
7 Conclusion and Outlook
A Appendix
A.1 Calculation of the skyrmion diameter
A.2 Micromagnetic simulation of the winding pair stability
Bibliography
Acknowledgements
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:30674 |
| Date | 16 November 2017 |
| Creators | Kopte, Martin |
| Contributors | Faßbender, Jürgen, Schmidt, Oliver G., Swagten, H. J. M., Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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