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Exchange bias in metamagnetic heterostructures
Zadorozhnii, Oleksii ; Schneeweiss, Oldřich (oponent) ; Uhlíř, Vojtěch (vedoucí práce)
Exchange bias is an intriguing physical phenomenon occuring at the interface of antiferromagnet (AF) and ferromagnet (FM) materials, which has already been widely applied in electronics and magnetic recording industry. Despite being intensely studied for a long time, the exact mechanism behind it remains an unsettled matter. This work presents an overview of the relevant studies documenting exchange bias in thin film bilayer systems, including both experimental evidence and theoretical models developed. The experimental tasks of this diploma thesis covered both manufacturing and measurement of different exchange bias model systems. An Fe/FeRh bilayer (here the FeRh layer features a phase transition from AF to FM at 360K), provides convenient tunability of the exchange bias. Next, the exchange bias and shape anisotropy effects were investigated in Fe/FeRh microstructures. Lastly, the presence of exchange bias was investigated between the coexisting FM and AF phases in submicron FeRh nanowires. The samples were fabricated using magnetron sputtering and E-beam lithography. All the presented systems were analyzed using Magneto-Optical Kerr Effect microscopy. Exchange bias was successfully found in the Fe/FeRh system nearly identical in magnitude and orientation to the results in literature, having an inferior FM-AF interface quality. Training effect as well as rotational asymmetry were also proven to exist within this system, solidifying the presence of exchange bias. In nanowires, significant exchange bias was measured between the coexisting FM and AF phases during cooling from the FM phase to the AF phase.
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Effect of ion beam irradiation and annealing on magnetic properties of FeRh nanostructures
Zadorozhnii, Oleksii ; Turčan, Igor (oponent) ; Staňo, Michal (vedoucí práce)
The first order phase transition from antiferromagnetic to ferromagnetic state in Fe50Rh50 at 370 K make it a suitable material for next generation spin electronic devices with a low power consumption. This work deals with the ways how the phase transition temperature of iron-rhodium (FeRh) can be tuned locally in thin films, using focused ion beam (FIB) and thermal annealing. FIB irradiation approach was chosen due to the fact that FeRh displays magnetic sensitivity to the degree of its chemical ordering, which is characteristic to all alloys of ferromagnetic and non-ferromagnetic metals. Thermal annealing enables the relaxation of the structure and restoration of its crystallinity. The magnetic patterns were manufactured using gallium-based FIB and annealed under ultra high vacuum. The topography as well as magnetic behaviour of these ion irradiated patterns were investigated using atomic and magnetic force microscopies at different temperatures, showing a clear dependence between ion irradiation dose and the magnetic response in pre- and post-annealed states.
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Parametrické pumpování jako zdroj krátkovlnných spinových vln
Pavelka, Dominik ; Zadorozhnii, Oleksii (oponent) ; Holobrádek, Jakub (vedoucí práce)
Spinové vlny mají potenciál sehrát klíčovou roli v oblasti moderních informačních technologií, jelikož mohou přenášet informaci s minimálními energetickými ztrátami. Pro účely implementace součástek založených na spinových vlnách do logických obvodů je nezbytné tyto součástky miniauturizovat. K tomuto účelu je zapotřebí krátkovlnných spinových vln a efektivních metod, jak je vybudit. Tato bakalářská práce se věnuje metodě buzení spinových vln parametrickým pumpováním. Pojednává o teorii potřebné pro pochopení této problematiky, a především zachycuje průběh plánování a provedení experimentu. Pro experiment byl navržen a vyroben vzorek s nanoanténami vhodnými pro parametrické pumpování krátkovlnných spinových vln. Výsledky měření na tomto vzorku potvrzují přítomnost parametricky pumpovaných spinových vln a zobrazují jejich závislost na frekvenci a amplitudě budicího pole. Práce přispívá k rozšíření našeho porozumění parametrickému pumpování spinových vln a bude na ni navazovat další výzkum využívající výsledků dosažených v této práci.
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Exchange bias in metamagnetic heterostructures
Zadorozhnii, Oleksii ; Schneeweiss, Oldřich (oponent) ; Uhlíř, Vojtěch (vedoucí práce)
Exchange bias is an intriguing physical phenomenon occuring at the interface of antiferromagnet (AF) and ferromagnet (FM) materials, which has already been widely applied in electronics and magnetic recording industry. Despite being intensely studied for a long time, the exact mechanism behind it remains an unsettled matter. This work presents an overview of the relevant studies documenting exchange bias in thin film bilayer systems, including both experimental evidence and theoretical models developed. The experimental tasks of this diploma thesis covered both manufacturing and measurement of different exchange bias model systems. An Fe/FeRh bilayer (here the FeRh layer features a phase transition from AF to FM at 360K), provides convenient tunability of the exchange bias. Next, the exchange bias and shape anisotropy effects were investigated in Fe/FeRh microstructures. Lastly, the presence of exchange bias was investigated between the coexisting FM and AF phases in submicron FeRh nanowires. The samples were fabricated using magnetron sputtering and E-beam lithography. All the presented systems were analyzed using Magneto-Optical Kerr Effect microscopy. Exchange bias was successfully found in the Fe/FeRh system nearly identical in magnitude and orientation to the results in literature, having an inferior FM-AF interface quality. Training effect as well as rotational asymmetry were also proven to exist within this system, solidifying the presence of exchange bias. In nanowires, significant exchange bias was measured between the coexisting FM and AF phases during cooling from the FM phase to the AF phase.
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Effect of ion beam irradiation and annealing on magnetic properties of FeRh nanostructures
Zadorozhnii, Oleksii ; Turčan, Igor (oponent) ; Staňo, Michal (vedoucí práce)
The first order phase transition from antiferromagnetic to ferromagnetic state in Fe50Rh50 at 370 K make it a suitable material for next generation spin electronic devices with a low power consumption. This work deals with the ways how the phase transition temperature of iron-rhodium (FeRh) can be tuned locally in thin films, using focused ion beam (FIB) and thermal annealing. FIB irradiation approach was chosen due to the fact that FeRh displays magnetic sensitivity to the degree of its chemical ordering, which is characteristic to all alloys of ferromagnetic and non-ferromagnetic metals. Thermal annealing enables the relaxation of the structure and restoration of its crystallinity. The magnetic patterns were manufactured using gallium-based FIB and annealed under ultra high vacuum. The topography as well as magnetic behaviour of these ion irradiated patterns were investigated using atomic and magnetic force microscopies at different temperatures, showing a clear dependence between ion irradiation dose and the magnetic response in pre- and post-annealed states.
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