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Vectorial Kerr magnetometry
Flajšman, Lukáš ; Veis,, Martin (referee) ; Urbánek, Michal (advisor)
Increased complexity of novel magnetic materials in the last decade has placed high demands on the manufacturing process as well as on the characterization. One of the possibilities for characterization of magnetic samples is to exploit the magneto-optical effects. The presented work uses the magneto-optical Kerr effect as a major characterization technique to probe the magnetic properties of samples. We have developed a mathematical model describing the effect of the magnetization on the polarized light and present an apparatus capable of measuring the response given by the light-matter interaction. The experimental results show the performance of the apparatus on the various magnetic systems including meta-stable iron layers, Stoner-Wohlfarth particles and magnetic vortices. The scanning vectorial Kerr magnetometer allowed us to probe the vector of magnetization with diffraction limited resolution below 500 nm.
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Magnetic vortex based memory device
Dhankhar, Meena ; Hrabec,, Aleš (referee) ; Veis,, Martin (referee) ; Urbánek, Michal (advisor)
Magnetické vortexy jsou charakterizovány směrem stáčení magnetizace a polarizací vortexového jádra, přičemž každá z těchto veličin nabývá dvojice stavů. Ve výsledku jsou tak k dispozici čtyři možné stabilní konfigurace, čehož může být využito v multibitových paměťových zařízeních. Tato dizertační práce se zabývá selektivním zápisem stavů magnetického vortexu v magnetickém disku pulzem elektrického proudu stejně jako jejich následným elektrickým čtením. Před samotnou realizací elektrických měření byla provedena statická měření přepínání stavů vortexu pomocí různých proudových pulzů v kombinaci s technikami MFM a následně MTXM. Následně byl realizován dynamický odečet stavu vortexu kompletně založený na elektrických měřeních. Ovládání cirkulace vortexu je založeno na geometrické asymetrii vytvořené oříznutím magnetického disku a vytvořením fazety. Plochý okraj disku definuje preferenční smysl stáčení cirkulace během procesu nukleace vortexu. Řízení polarity se obvykle provádí ve dvou krocích. V prvním kroku, homogenně magnetizovaná vrstva s kolmou magnetickou anizotropií umístěná na dně disku definuje výchozí polaritu vortexu v době nukleace. V druhém kroku, je-li to nutné, je polarita vortexu přepnuta pomocí rychlého proudového pulzu. Proto je možné nastavit požadovaný stav cirkulace vysláním nanosekundového pulsu s nízkou amplitudou, následované nastavením polarity pikosekundovým pulsem s vysokou amplitudou. Stavy vortexů jsou pak detekovány elektrickou spektroskopií prostřednictvím anizotropní magnetorezistence. Vzorky pro všechna statická a dynamická měření byly připraveny pomocí elektronové litografie v kombinaci s lift-off procesem.
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Design of Optically Detected Magnetic Resonance (ODMR) Spectrometer
Schneider, Martin ; Veis, Martin (referee) ; Neugebauer, Petr (advisor)
Diplomová práce se zabývá návrhem a sestavením nového spektrometru opticky detekované magnetické rezonance (ODMR) modifikací stávajícího spektrometru magnetického kruhového dichroismu (MCD) přivedením mikrovlnného ozařování. Je navrhnut nový držák vzorku umožnující osvětlení jak viditelným světlem, tak mikrovlnným zářením. Pro přivedení vlnění o nižších frekvencích je navržena anténa, určená k umístění pod vzorkem. Schopnosti celého systému jsou demonstrovány na sloučenínách kovových komplexů.
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Mapping of changes in optical and magneto-optical responses of Ni-Mn-Ga thin films across martensitic transformation and strain relaxation
Makeš, Matěj ; Veis, Martin (advisor) ; Zemen, Jan (referee)
This thesis studies optical and magneto-optical responses of thin epitaxial Ni-Mn- Ga films prepared by magnetron sputtering. The relative permittivity tensor spectra were computed from the spectroscopic ellipsometry data measured both without the external magnetic field and in the out-of-plane magnetic field configuration. For one of the thin film samples, measurements across martensitic transformation were performed and temperature-hysteresis was observed. The analysis of the obtained spectra for thickness- varied series of samples clearly demonstrated the influence of substrate-induced strain and revealed a strong correlation between the out-of-plane lattice parameter and the properties of the obtained spectra. 1
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Optical and magneto-optical properties of topological and Dirac materials
Tikuišis, Kristupas Kazimieras ; Veis, Martin (advisor) ; Slobodeniuk, Artur (referee) ; Erlingsson, Sigurdur Ingi (referee)
Kristupas Kazimieras Tikuišis, Department of Optoelectronics and Magneto- optics, Institute of Physics of Charles University Doctoral thesis: Optical and magneto-optical properties of topological and Dirac materials Supervisor: RNDr. Martin Veis, Ph.D., Department of Optoelectronics and Magneto-optics Advisers: RNDr. Roman Antoš, Ph.D., Department of Optoelectronics and Magneto-optics; Milan Orlita, Ph.D., National Laboratory of High Magnetic Fields LNCMI - Grenoble, CNRS (France) Abstract: Dirac materials exhibit unusual properties that attract interest both for practi- cal applications and fundamental reseach of exotic and relativistic physics. This thesis aims to systematically study basic optical and magneto-optical proper- ties of several members of these materials, namely the lead tin salts crystalline topological insulators and graphene. Non-destructive experimental techniques of spectroscoipic ellipsometry and FTIR magneto-optical spectroscopy were used to perform measurements from IR to UV spectral regions. A four-band Hamilto- nian model was derived to describe the most important band structure features of PbSnSe system placed in a magnetic field. This allowed to extract the band structure and topological parameters of the investigated samples. Extensive mod- eling results based on...
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Magnetooptické studium vlivu zárodečné vrstvy na formování magnetických vlastností tenkých vrstev La2/3Sr1/3MnO3
Melzer, Aleš ; Veis, Martin (advisor) ; Zahradník, Martin (referee)
The impact of film thickness on optical and magneto-optical properties of La2/3Sr1/3O3 (LSMO) thin films was studied by optical and magneto-optical methods. A series of LSMO samples with increasing thicknesses was pre- pared by pulsed laser deposition on a silicon substrate with a Ca2Nb3O10 seed layer. The topology of both the substrates and the deposited films was examined by atomic force microscopy. The samples were subsequently analy- sed by spectroscopic ellipsometry and magneto-optical spectroscopy. The off- diagonal elements of the permittivity tensor of each layer were afterwards de- termined numerically from these measurements. The obtained spectra exhibi- ted spectroscopic structures found in epitaxial LSMO films grown on SrTiO3 (STO), reflecting good crystalline quality of investigated samples. Effects re- lated to gradual strain relaxation with increasing film thickness were observed on the spectra.
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FDTD simulace funčkních fotonických struktur
Novák, Ondřej ; Veis, Martin (advisor)
This thesis aims to (i) design and optimize the geometry of magneto-photonic crystal based on ferromagnetic garnet in order to resonantly enhance the magneto-optical re- sponse, (ii) to explore the possibility of using magnetic shape memory alloy to build an optically active photonic element, using advanced FDTD modeling. A Faraday rotation of 180◦ was reached but with low values of transmissivity. An investigation of the origin of such high values of Faraday rotation led to a conclusion that such structure has to be highly sensitive towards a change of a refractive index of its surroundings. This was confirmed, and so further development of this structure can lead to an efficient concentra- tion detector. Three designs of optically active element utilizing deformation of magnetic shape memory material in the external magnetic field were numerically simulated. Two designs (photonic crystal with cylindric holes in a hexagonal lattice and self-standing foil with cylindric holes in a square lattice) proved to be efficient and worth of further development. 1
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Kontrola magnetické anizotropie v multivrstvách Pt/Co/Pt
Nowak, Lukáš ; Veis, Martin (advisor)
This thesis aims to explore the effect of in situ ion gun etching on magnetic proper- ties, such as perpendicular magnetic anisotropy, of Pt/Co/Pt multilayers. Perpendicular magnetic anisotropy is of interest due to its importance in spintronic application. Calibration spectroscopic ellipsometry measurements of Pt and Co layers to obtain sputter yields of respective magnetron targets were performed as a first step. After that, ten Pt/Co/Pt multilayers with different Co and top Pt layer thicknesses were prepared. Five of these samples were etched by the ion gun, mounted inside of the magnetron chamber, during different stages of the deposition. To characterize the prepared samples, experimental and modeled Kerr rotation spectra were confronted. This provided an insight into the cross-sections of the investigated samples. Magnetic hysteresis loops measured by vibrating sample magnetometer and Kerr rotation setup demonstrated higher coercive field and change of the slope of the loop induced by ion etching. When compared to the obtained cross-sections, a correlation between the change of magnetic loops and intermixing of Pt and Co at the interface was visible. This intermixing was higher in samples treated by the ion gun. 1
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Spectroscopic studies of new generation of optical and magneto-optical materials
Butková, Eva ; Veis, Martin (advisor) ; Chlan, Vojtěch (referee) ; Zemen, Jan (referee)
Title: Spectroscopic studies of new generation of optical and magneto-optical materials Author: Eva Butková Department / Institute: Institute of Physics of Charles University. Department of Materials Science and Technology of Nagaoka University of Technology. Supervisors of the doctoral thesis: RNDr. Martin Veis, Ph.D., Division of Magneto-optics, Institute of Physics of Charles University Dr. Takayuki Ishibashi, Ph.D., Department of Materials Science and Technology, Nagaoka University of Technology Abstract: In recent years, novel optical and magneto-optical devices have been proposed. This ranges from integrated photonic devices such as 3D holographic displays to magnetic recording, non- reciprocal photonic devices such as optical isolators and circulators or high-energy X-ray/gamma ray detectors. These devices, however, require suitable materials with tunable optical and magneto-optical properties. Presented thesis aims to systematically study such materials, namely GdxFe(100-x), magnetic garnets (Y3-xBixFe5O12, Nd2BiFe(5-x)GaxO12, Nd0.5Bi2.5Fe(5-x)GaxO12) and Ce(0.95-x)HfxCo0.05O(2-δ). Systematic study is carried out by the combination of experimental methods of spectroscopic ellipsometry, magneto-optical Kerr effect spectroscopy and Faraday effect spectroscopy. Experimental data are confronted to...
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Physical properties of doped and non-doped Tb3Fe5O12 studied by optical spectroscopies
Vančík, Michal ; Veis, Martin (advisor) ; Mistrík, Jan (referee)
This thesis focuses on systematic study of optical and magneto-optical properties of non-doped and doped Tb3Fe5O12 thin films, on gadolinium gallium garnet and silicon substrates. Spectroscopic ellipsometry measurements were performed to obtain optical properties, thicknesses and surface roughness values of studied samples. The magneto- optical properties were investigated using the Kerr and Faraday effect measurements. Obtained experimental data were used to calculate the spectral dependence of the off- diagonal components of permittivity tensor. The results were compared with literature, and the effect of doping was discussed. On three samples, the spectral magneto-optical Kerr rotation hysteresis loops were measured, for the purpose of separating the individual contributions of sublattices. The analysis revealed that the method is probably insensitive to sublattice contributions but is sensitive to the contributions of regions with different magnetic anisotropy within the deposited layer. 1
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