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Magneto-optical study of the dynamic properties of magnetic nanostructures and nanostructured metamaterials
Flajšman, Lukáš ; Chumak, Andrii (referee) ; Revelosona, Dafiné (referee) ; Spousta, Jiří (advisor)
Magnonika je novým odvětvím výzkumu, který se zabývá fyzikou spinových vln. Magnonika jako vědní obor nabízí nové možnosti například v nediskrétních výpočtech na základě vlnového charakteru spinových vln. Při výrobě magnonických prvků klasickými metodami není možné příliš měnit charakter materiálů, ze kterých jsou jednotlivé prvky vyrobeny. Tento fakt silně omezuje univerzálnost vyrobených struktur. Cílem této práce je aplikovat nový typ materiálu do oboru magnoniky. Specifikum daného materiálu je možnost zápisu magnetických struktur pomocí iontového svazku. Ukazuje se, že tyto struktury mají velice zajímavé magnetické vlastnosti, které lze velice přesně řídit právě strategií ozařování iontovým svazkem. Na základě fázově rozlišené Brillouinovy spektroskopie jsme získali disperzní relaci spinových vln v tomto systému a tím i důležité parametry systému. Pozorování podkládáme mikromagnetickými simulacemi a analytickými modely. Vlastnosti systému pro magnonické aplikace prezentujeme na třech prototypických sadách struktur, které nelze vyrobit pomocí klasických materiálů.
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Losses Analysis in Electric Machines under Special Conditions
Bulín, Tomáš ; Rafajdus, Pavol (referee) ; Skala, Bohumil (referee) ; Ondrůšek, Čestmír (advisor)
This thesis deals with the analysis of magnetic losses in electrical machines and the possibilities of their measurement. Magnetically soft and hard materials are very prone to changing magnetic properties. They can be changed simply by changing the temperature of the material or different stresses induced in the material, resulting in different results. These changes are important to keep in mind when an electric machine is being designed. The original parameters of the affected materials can be restored by annealing or grinding. These methods release the induced stresses within the material. Due to these effects, it is also important to know how to measure magnetic parameters. Each way has its own specifics and has a certain error of the measurement. When the machines for higher efficiency, rpm or higher temperatures are designed, it is advisable to know how their magnetic properties changed. This thesis deals with the properties of different materials, their measurements and finally simulation of the chosen electric machine with the application of the measured results.
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Ground state investigations of Ce and U intermetallic compounds
Bartha, Attila ; Prokleška, Jan (advisor) ; Detlefs, Blanka (referee) ; Michor, Herwig (referee)
Title: Ground state investigations of Ce and U intermetallic compounds Author: Attila Bartha Department: Department of Condensed Matter Physics Supervisor: RNDr. Jan Prokleška, Ph.D., Department of Condensed Matter Physics Abstract: Rare earth and actinide intermetallic compounds offer a plethora of interesting physical properties due to the varied behavior of f -electrons together with numerous interactions these electrons are exposed to. In this thesis we address a broad spectrum of ground state investigations on CePd2X3 (X=Zn, Ga) and (Ce,U)nTIn3n+2 (T=Rh, Ir) compounds. Single crystals of CePd2Zn3 and CePd2Ga3 compounds were synthesized for the first time using Bridgman method. CePd2Ga3 revealed a ferromagnetic transition with TC = 6.7 K with a strong magnetocrystalline anisotropy. CePd2Zn3 orders antiferromagnetically below TN = 1.9 K. Results of magnetization measurements on Ce2IrIn8 revealed effective magnetic moment µeff = 2.45µB/Ce3+ and a paramagnetic Curie temperature θP = −31 K. Decomposition of Hall resistivity ρxy(B) into NHE and AHE revealed a predom- inance of AHE in the temperature range from 60 K up to 100 K. Ce2RhIn8 was studied by means of magnetic field and angle dependent magnetization and heat capacity measurements. The resulting phase diagram reveals a complete unfold- ing and...
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Magnetic Energy Harvesting Device for Low Excitation Vibration
Szabó, Hugo ; Singule, Vladislav (referee) ; Rubeš, Ondřej (advisor)
This bachelor theasis is focused on a concept of a magnetic energy harvesting device for low exitation frequencies. The device is made out of mechanical and electrical part where mechanical part is made out of two levitating magnets that repent each other and an electrical part is made out of magnetic circuit and a coil whose relative motion induces voltage in the coil. Mathematical model is made in Matlab, Simulink and FEMM. Construction model is made in Inventor.
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Passive axial magnetic bearing
Dostál, Patrik ; Štěpánek, Vojtěch (referee) ; Pruša, Radomír (advisor)
The goal of the bachelor thesis is to measure the characteristics of a passive magnetic bearing. The practical part of the thesis consists of two segments – experimental measurement of properties of a passive axial magnetic bearing and a simulation of this bearing using the finite element method in the FEMM application. The simulation also dealt with the effects of temperature on the bearing. It was discovered that high temperatures considerably lower the axial stiffness of the magnetic bearing. Other effects on the stiffness of the bearing were taken into consideration, especially the dimensions of used magnets and the distance between them. The values that were determined by the experimental measurement and the FEMM simulation were mutually compared. The analysed bearing was built for use in a seal-less centrifugal pump. The values determined by the simulation and the measurement were applied to practical use in pumps. A part of the thesis was concerned with a research on passive magnetic bearings. The research dealt with the principle of the bearings, their structure and their application.
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Popularisation of Science in the Czech Republic
Holčapková, Martina ; Walek, Agata (referee) ; Baumgartnerová, Alena (advisor)
Bakalářská práce se zabývá tématem popularizace vědy. Cílem práce je definovat subjekty zabývající se popularizací vědy a zjistit informovanost veřejnosti o daném tématu. První část práce je zaměřena na definici termínu popularizace vědy. V druhé části jsou popsány rozdíly v učení dospělých a dětí. Třetí část ukazuje subjekty popularizace vědy a následující kapitola, založená na dotazníku, popisuje povědomí obyvatel Brna a jeho okolí o možnostech popularizace vědy. Závěrečná kapitola se věnuje tvorbě popularizačně naučného programu zaměřeného na téma elektřina a magnetismus.
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Theory of spin-dependent transport in magnetic solids
Wagenknecht, David ; Turek, Ilja (advisor) ; Minár, Ján (referee) ; Šipr, Ondřej (referee)
of doctoral thesis Theory of spin-dependent transport in magnetic solids David Wagenknecht Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University 2019 Theoretical and ab initio description of realistic material behavior is complicated and combinations of various scattering mechanisms or temperature effects are often neglected, although experimental samples contain impurities and modern electronics work at finite temperatures. In order to remove these knowledge gaps, the alloy analogy model is worked out in this thesis and implemented within the fully relativistic tight- binding linear-muffin-tin orbital method with the coherent potential approximation. This first-principles framework is shown to be robust and computationally efficient and, consequently, employed to investigate bulk solids and their spintronic applications. Unified effect of phonons, magnons, and alloying gives agreement with literature for temperature-dependent electrical transport (longitudinal and anomalous Hall resistivities) and scattering mechanisms are explained from electronic structures. Moreover, novel data help to identify defects in real samples and experimentally hardly accessible quantities are presented, such as spin polarization of electrical current. Calculated results for both zero...
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Electromagnetic power actuators
Kadlecová, Lucie ; Vorel, Pavel (referee) ; Folprecht, Martin (advisor)
This master thesis focuses on literature research of problematics linked to power actuators working on electromagnetic principle to accelerate metal projectiles. It’s goal is mathematical analysis and constuction of selected type of electromagntic power actuator – induction coilgun
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Elektronové vlastnosti sloučenin RPd5Al2
Zubáč, Jan ; Javorský, Pavel (advisor)
We have studied magnetic properties of the intermetallic NdPd5Al2 com- pound by means of specific heat and magnetization measurements and neutron scattering. The compound crystallizes in the tetragonal I4/mmm space group with lattice parameters a =4.147 ˚A and c =14.865 ˚A, orders antiferromagnet- ically below TN =1.3 K and presents large magnetocrystalline anisotropy due to the crystal-field effects. The obtained magnetic phase diagram is charac- terized by two distinct magnetically ordered phases similarly to structurally re- lated tetragonal RTX5 and R2TX8 compounds. The zero-field antiferromagnetic phase is characterized by the propagation vector k = (1 2 00) and antiferromag- netic coupling of Nd moments along the teragonal c-axis with the amplitude of magnetic moments of 2.22 µB/Nd as was revealed by neutron diffraction. The transition from the paramagnetic to magnetically ordered in zero field is the first-order phase transition. The CF excitations in NdPd5Al2 were detected by means of INS at 3.0 meV, 7.4 meV, 8.6 meV and 17.1 meV. We further compare our findings about CF in NdPd5Al2 obtained from INS, susceptibility analysis and first-principles calculations and confront them with the experimental mag- netization and magnetic specific heat data. Our results will be also discussed with respect to related...
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Hybrid Energy Harvesting Device
Rasocha, David ; Rubeš, Ondřej (referee) ; Hadaš, Zdeněk (advisor)
This bachelor theasis is focuses on the design of a hybrid piezoelectric vibratory genera-tor. The main idea is to place a permanent magnet on the end of the piezoelectric beam and to place the coil appropriately in order to make a electromagnetic generator. The coil will generate a electrical voltage on load, when the magnetic field is passing throught coil. The piezoelectric beam will also generate voltage, depending on its deformation. For modeling, Femm, Matlab and Simulink will be used.
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