GHz Magnetization Dynamics in X-ray PhotoEmission Electron Microscopy (XPEEM)
[eng] This thesis presents the recent results achieved during my Ph.D. This is a research project in the field of condensed matter physics, under the supervision of Dr. Michael Foerster of the ALBA Synchrotron and Dr. Ferran Macià from the University of Barcelona, during November 2020 to February 20...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2024 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/216255 |
| Acceso en línea: | https://hdl.handle.net/2445/216255 http://hdl.handle.net/10803/692455 |
| Access Level: | acceso abierto |
| Palabra clave: | Espectroscòpia de raigs X Microscòpia electrònica Piezoelectricitat Dicroisme circular X-ray spectroscopy Electron microscopy Piezoelectricity Circular dichroism |
| Sumario: | [eng] This thesis presents the recent results achieved during my Ph.D. This is a research project in the field of condensed matter physics, under the supervision of Dr. Michael Foerster of the ALBA Synchrotron and Dr. Ferran Macià from the University of Barcelona, during November 2020 to February 2024. This thesis is based on a collection of articles combined with an overview and a discussion. In general, magnetic systems which are influenced by different energy factors, realize a final state that tries to minimize the total energy. This can produce diverse magnetic patterns that deviate from uniform alignment. Observing and controlling the evolution of magnetization is vital for the development of fast devices and often requires operations on sub-nanosecond time scales. The main objective of this thesis is to generate and observe magnetization dynamics at the micro/nano scale in different systems of thin magnetic layers from acoustic waves. This approach represents a low-energy method compared to other conventional approaches to induce dynamics in magnetic systems. X-ray photoemission electron microscopy (XPEEM) is used to observe the dynamics of magnetic systems under the effect of acoustic waves. This work is structured in seven chapters. The first chapter consists of a brief introduction and the objectives of the thesis. Chapter 2 provides the general introduction into the field of magnetism that provides details on the origin of magnetism in a particular material. There are various energies present in magnetic materials, either intrinsic or extrinsic, that adjust the ground state of the material. The global magnetic behavior is governed by the balance between these energies, giving rise to various magnetic configurations in the system. In the third chapter, knowledge about the synchrotron and synchrotron light is presented along with the different sections of the synchrotron that lead to the generation of X-rays. PEEM uses these X-rays to obtain images of the magnetic behavior of materials. This mechanism is discussed below, which includes the instrumentation of the PEEM configuration and the factors that affect its spatial resolution. Various characterization techniques can be performed using XPEEM, such as XAS, XMCD, XMLD, XPS, etc. to determine the occupation states in magnetic systems. In addition, since the thesis was mainly carried out in the Alba synchrotron light facility, several attributes related to this installation are also presented. Chapter four discusses the importance of tuning magnetization in materials to improve their properties for various applications. It explores different methods to understand and optimize magnetization dynamics within materials. The chapter is divided into three parts. First, it provides an overview of the state of the art and the underlying physics of magnetization dynamics. Second, it analyzes the role of surface acoustic waves (SAW) in the manipulation of magnetization dynamics, including the most relevant studies. Finally, the experimental setup required to combine SAW generation in magnetic devices together with XPEEM imaging is explored, with the aim of observing and analyzing the magnetization dynamics, and how the magnetization is coupled to acoustic waves. In the fifth chapter, a detailed summary of all the articles included in this thesis is presented, followed by the sixth chapter which includes all the articles. Among these papers, one has been published in the journal Ultramicroscopy and the other two have already been submitted and are under review in Phys. Rev. Lett. and Phys. Rev. Research. We have observed that the strain due to SAW induces magnetization dynamics in both ferromagnetic and antiferromagnetic systems and both systems exhibit comparable efficiency. We designed and built a high frequency connection for the XPEEM microscope system that allows studying excitations at higher frequencies (>1 GHz) and used it to study magneto-acoustic waves (combination of magnetic waves and acoustic waves) in ferromagnetic systems such as Ni and Co and to determine their magnetoelastic coupling in this regime. Finally, the conclusions are summarized and the perspectives are added in the seventh chapter. This thesis presents a new approach to generate magnetoacoustic waves in magnetic thin layers based on the magnetoelastic interaction. On the one hand in antiferromagnetic materials, offering potential applications in data storage and on the other in ferromagnetic materials, where we observe the weakening of waves at frequencies above 1 GHz; suggesting that more work is needed to address this. Striking variations in wave amplitudes at specific frequencies in different ferromagnetic systems suggest diverse interactions between magnetization waves and acoustic waves. In addition, the new system designed for the XPEEM microscope at the ALBA offers opportunities to make measurements with time resolution, such as studies of magnetization dynamics, domain walls and skyrmion motion using ultra-short current pulses. These pathways promise to develop new nanomagnetic devices for future data storage applications, emphasizing the importance of continued exploration in both fundamental and technological areas. |
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