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Imaging of metamagnetic thin films using TEM
Hajduček, Jan ; Buršík,, Jiří (oponent) ; Uhlíř, Vojtěch (vedoucí práce)
Complex magnetic materials at the nanoscale are essential in many areas of modern devices, such as digital memories or sensors. Novel technological approaches require the control and understanding of modern magnetic materials down to the atomic scale. One possibility is to exploit high-resolution transmission electron microscopy (TEM), characteristic for its outstanding subatomic resolution. This thesis investigates the options of TEM imaging of metamagnetic materials. These materials are characteristic by displaying coexistence of magnetic phases upon external control. Thin films of metamagnetic FeRh are used as an experimental platform to investigate the various aspects of TEM imaging. FeRh undergoes the metamagnetic phase transition from antiferromagnetic to ferromagnetic phase upon heating. We start with evaluating the sample fabrication processes suitable for our system, which is essential for successful TEM analysis. The differential phase contrast (DPC) technique in TEM is used for the magnetic analysis due to its direct access to the sample magnetic field configuration. An in-depth discussion of DPC signal formation is presented, which is crucial for understanding and analysis of resulting images. Furthermore, we perform structural, chemical, and particularly magnetic imaging of both magnetic phases present in FeRh. Finally, the process of in-situ heating of metamagnetic FeRh lamellae is presented.
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Magnetic properties of self-assembled FeRh nanomagnets
Motyčková, Lucie ; Fruchart, Olivier (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
Magnetic nanoparticles and nanostructured materials are of great promise in many domains, including biomedicine, environmental remediation, or energy harvesting. Therefore, there is an ever-growing interest in their unique nanoscale functionalities as well as in the development of viable fabrication routes. This thesis investigates a self-assembly route, specifically solid-state dewetting of thin films, to produce epitaxial nanoisland arrays of the FeRh alloy on different single-crystal substrates. It is shown that using this fabrication route, the metamagnetic phase transition is preserved in nanoscale confined geometries. The morphology and magnetic properties of the self-assembled FeRh nanomagnets are characterized by a combination of experimental techniques and modeling, finding that their equilibrium shapes and magnetic order are closely interconnected. Furthermore, a route for obtaining free-standing nanoparticles is devised, which could potentially allow using metamagnetic nano-objects in cell cultures and biomedicine in general. To do so, the supported FeRh nanomagnets are released from the substrate via chemical wet etching. The behavior of the nanoparticles and their response to temperature cycling and magnetic field is subsequently studied in a liquid environment. The metamagnetic properties of separated nanoparticles are characterized using vibrating sample magnetometry.
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Imaging of metamagnetic thin films using TEM
Hajduček, Jan ; Buršík,, Jiří (oponent) ; Uhlíř, Vojtěch (vedoucí práce)
Complex magnetic materials at the nanoscale are essential in many areas of modern devices, such as digital memories or sensors. Novel technological approaches require the control and understanding of modern magnetic materials down to the atomic scale. One possibility is to exploit high-resolution transmission electron microscopy (TEM), characteristic for its outstanding subatomic resolution. This thesis investigates the options of TEM imaging of metamagnetic materials. These materials are characteristic by displaying coexistence of magnetic phases upon external control. Thin films of metamagnetic FeRh are used as an experimental platform to investigate the various aspects of TEM imaging. FeRh undergoes the metamagnetic phase transition from antiferromagnetic to ferromagnetic phase upon heating. We start with evaluating the sample fabrication processes suitable for our system, which is essential for successful TEM analysis. The differential phase contrast (DPC) technique in TEM is used for the magnetic analysis due to its direct access to the sample magnetic field configuration. An in-depth discussion of DPC signal formation is presented, which is crucial for understanding and analysis of resulting images. Furthermore, we perform structural, chemical, and particularly magnetic imaging of both magnetic phases present in FeRh. Finally, the process of in-situ heating of metamagnetic FeRh lamellae is presented.
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Magnetic properties of self-assembled FeRh nanomagnets
Motyčková, Lucie ; Fruchart, Olivier (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
Magnetic nanoparticles and nanostructured materials are of great promise in many domains, including biomedicine, environmental remediation, or energy harvesting. Therefore, there is an ever-growing interest in their unique nanoscale functionalities as well as in the development of viable fabrication routes. This thesis investigates a self-assembly route, specifically solid-state dewetting of thin films, to produce epitaxial nanoisland arrays of the FeRh alloy on different single-crystal substrates. It is shown that using this fabrication route, the metamagnetic phase transition is preserved in nanoscale confined geometries. The morphology and magnetic properties of the self-assembled FeRh nanomagnets are characterized by a combination of experimental techniques and modeling, finding that their equilibrium shapes and magnetic order are closely interconnected. Furthermore, a route for obtaining free-standing nanoparticles is devised, which could potentially allow using metamagnetic nano-objects in cell cultures and biomedicine in general. To do so, the supported FeRh nanomagnets are released from the substrate via chemical wet etching. The behavior of the nanoparticles and their response to temperature cycling and magnetic field is subsequently studied in a liquid environment. The metamagnetic properties of separated nanoparticles are characterized using vibrating sample magnetometry.
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