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Preparation and characterization of substituted Y ferrites in the form of ceramics and thin films
Pulmannová, Dorota ; Nižňanský, Daniel (advisor) ; Prokleška, Jan (referee)
Title: Preparation and characterization of substituted Y ferrites in the form of ceramics and thin films Author: Dorota Pulmannová Department: Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague Supervisor: RNDr. Daniel Nižňanský, Ph.D. Consultant: Ing. Josef Buršík, CSc. Abstract: In this work we describe a preparation and characterization of a hexagonal ferrite series with composition BaSrCoZnXFe11O22 where X=Fe, Al, Ga, In and Sc. We have prepared these ferrites in the powder and ceramic form using the citrate synthesis and in the thin film form using the chemical solution deposition method. Using the powder neutron diffraction we have found that the sample containing only Fe has collinear magnetic structure that belongs to the C2/m or C2'/m' group. Magnetic structure of the samples substituted with In and Sc is similar, but the magnetic moments of the 18hVI site atoms are not aligned parallely with the other moments. Magnetic structure of Ga-substituted sample is different, it is modulated with a propagation vector k ≈ (0, 0, 3/4). Propagation vector of the Al-substituted ferrite is k ≈ (0, 0, 3/2). Substituting elements show strong preferences for the cation sites. Al and Ga prefer the 3bVI site, Zn prefers the tetrahedral 6cIV and In and Sc prefer the 6cVI site. Room...
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Magnetic excitations in cerium compounds
Vlášková, Kristina ; Javorský, Pavel (advisor) ; Prchal, Jiří (referee)
Title: Magnetic excitations in cerium compounds Author: Kristina Vlášková Department: Department of Condensed Matter Physic Supervisor: doc. Mgr Pavel Javorský, Dr., Department of Condensed Matter Physics Abstract: Thanks to presence of only one electron in 4f shell of cerium ion, Ce based compounds reveal wide range of exceptional magnetic properties like valence fluctuations, magnetic ordering or spin glass behavior. In present thesis we mainly focus on tetragonal CeCuxAl4-x system and its magnetic behavior. Former results of inelastic neutron experiments opened discussion about energy levels of cerium ions in CeCuAl3. Except two crystal field excitations also one additional energy level was present, phenomenon of vibron quasi-bound state was proposed to explain observed energy structure. Measurement and analysis of specific heat and neutron inelastic scattering on compounds with various Cu content should help to understand phenomenon of vibron state and also its development with Cu/Al concentration. Another two types of cerium compounds will be investigated in means of specific heat and resistivity measurement, polycrystalline sample of CePt4Al and single crystal of Ce3Ru4Al12. Preparation, characterization and measurement of low temperature properties are subjects of this work. Results will be discussed...
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Magneto-optic response of layered media
Kunt, Ota ; Ostatnický, Tomáš (advisor) ; Antoš, Roman (referee)
Optical response of materials strongly depends on their magnetic properties. This phenomenon is also used in materials in the form of thin layers and multi- layers. Using cited literature we summarize theory needed to calculate magneto- optical response of multilayers. The calculation is based on Maxwell equations and magnetic materials are described with effective permittivity tensor. Jones formalism is used to describe polarised light and Yeh formalism is used to de- scribe multilayer response. A program using presented theory was developed and calculations for concrete structure were made. Multilayer parameters were cho- sen to correspond with those of a sample whose magneto-optical response was measured at the Department of Chemical Physics and Optics, MFF UK. 1
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Nanostructures and Materials for Antiferromagnetic Spintronics
Reichlová, Helena ; Novák, Vít (advisor) ; Ferguson, Andrew (referee) ; Kunc, Jan (referee)
This thesis is focused on two open problems of antiferromagnetic (AFM) spintronics: manipulation of AFM coupled moments and development of new materials combining AFM and semiconductor properties. We present three particular methods enabling AFM moments manipulation. The rst method, based on the exchange spring effect in an AFM/FM double layer, strongly de- pends on the AFM layer thickness and temperature. We systematically vary these two parameters and identify the conditions when AFM moments can be manip- ulated. By the second method, cooling an AFM in a magnetic eld through the critical temperature, we prove the concept of a fully AFM-based (containing no FM) spintronic device. The last studied method is based on current induced effects in nanostructures containing an AFM. By systematic study of samples with and without AFM we demonstrate the ability of AFM moments to absorb a current induced torque. Relying neither on a FM nor on cooling in magnetic eld, this method represents an elegant way of AFM moments manipulation. In the second experimental part new materials for AFM spintronics are discussed, and one representative example, CuMnAs, is studied in detail. Characterization of bulk and epitaxial CuMnAs is presented and rst spintronic functionality is shown. Powered by TCPDF (www.tcpdf.org)
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Electron properties of the substituted cerium compounds
Klicpera, Milan ; Javorský, Pavel (advisor) ; Hiess, Arno (referee) ; Michor, Herwig (referee)
Title: Electron properties of the substituted cerium compounds Author: Milan Klicpera Department: Department of Condensed Matter Physics Supervisor: doc. Mgr. Pavel Javorský Dr. Abstract: The subject of this work is the study of vibron states in tetragonal CeCuAl3 and CePd2Al2 compounds and their development with the substitution of constituent elements. After the preparation of single crystals and polycrystalline samples, the careful chemical and structural characterization was done. The structural, magnetic and superconducting phase transitions in samples were observed and thoroughly investigated. The crucial experiments were performed using the elastic and inelastic neutron scattering techniques leading to the refinement of magnetic structures in CeCuAl3, CePd2Al2 and CePd2Ga2. The energy spectra of substituted Ce(Cu,Al)4 and CePd2(Al,Ga)2 compounds were studied as well allowing to determine the crystal field excitations and their interaction with phonons (vibron states) in these materials. Keywords: cerium internetallic compounds, vibron states, electronic properties, neutron scattering
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Nanoparticles based on 3d metal oxides - correlation of structure and magnetism
Kubíčková, Simona ; Kalbáčová Vejpravová, Jana (advisor) ; Cannas, Carla (referee) ; Svoboda, Pavel (referee)
Title: Nanoparticles based on 3d metal oxides - correlation of structure and magnetism Author: RNDr. Simona Kubíčková Department: Institute of Physics CAS, v.v.i. Supervisor: doc. RNDr. Jana Kalbáčová Vejpravová, Ph.D., Institute of Physics CAS, v.v.i. Abstract: The thesis is focused on the correlation of the magnetic response of iron oxide nanoparticles (NPs) with their internal structure. Several complementary methods were used and compared that bring insight into the relative crystallinity of the investigated NPs. The main goal was devoted to the elucidation of the origin of the so-called spin canting angle determined by In-field Mössbauer Spectroscopy (IFMS) by examination of samples with different internal structure. It has been observed that the IFMS is not an unambiguous method to study the surface effects in the NPs as the IFMS is sensitive only to the average value of all spins and does not distinguish between the surface and core effects. Moreover, the IFMS was performed on the epsilon phase of the iron(III) oxide NPs in order to inspect the peculiar behavior of this phase in an external magnetic field. Keywords: iron oxide nanoparticles, magnetism, In-field Mössbauer Spectroscopy, spin canting
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Nanostructures and Materials for Antiferromagnetic Spintronics
Reichlová, Helena ; Novák, Vít (advisor)
This thesis is focused on two open problems of antiferromagnetic (AFM) spintronics: manipulation of AFM coupled moments and development of new materials combining AFM and semiconductor properties. We present three particular methods enabling AFM moments manipulation. The rst method, based on the exchange spring effect in an AFM/FM double layer, strongly de- pends on the AFM layer thickness and temperature. We systematically vary these two parameters and identify the conditions when AFM moments can be manip- ulated. By the second method, cooling an AFM in a magnetic eld through the critical temperature, we prove the concept of a fully AFM-based (containing no FM) spintronic device. The last studied method is based on current induced effects in nanostructures containing an AFM. By systematic study of samples with and without AFM we demonstrate the ability of AFM moments to absorb a current induced torque. Relying neither on a FM nor on cooling in magnetic eld, this method represents an elegant way of AFM moments manipulation. In the second experimental part new materials for AFM spintronics are discussed, and one representative example, CuMnAs, is studied in detail. Characterization of bulk and epitaxial CuMnAs is presented and rst spintronic functionality is shown. Powered by TCPDF (www.tcpdf.org)
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Elektronové vlastnosti sloučenin RPd5Al2
Zubáč, Jan ; Javorský, Pavel (advisor) ; Čermák, Petr (referee)
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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Kritické chování v magnetických fázových diagramech uranových sloučenin
Opletal, Petr ; Prokleška, Jan (advisor)
Title: Critical behavior in magnetic phase diagrams of uranium compounds Author: Bc. Petr Opletal Department: Department of Condensed Matter Physics Supervisor: RNDr. Jan Prokleška, Ph.D., Department of Condensed Matter Physics Abstract: This work is focused on study of phase diagrams and related critical effects in the pseudoternary UCo1-xRuxAl compound. Three single crystals of nominal composition UCo0.99Ru0.01Al, UCo0.995Ru0.005Al and UCo0.9975Ru0.0025Al have been prepared by Czochralski method in triarc furnace. Quality of single crystals was checked by EDX analysis, Laue method and XRPD. For UCo0.99Ru0.01Al Curie temperature was determined as TC = 16 K. UCo0.995Ru0.005Al shows transition from paramagnetic to ferromagnetic phase at TC= 4.5 K and at higher temperatures we observe a metamagnetic transition of first order with a critical field HC = 0.04 T. UCo0.9975Ru0.0025Al is paramagnetic to low temperatures with metamagnetic transition of first order and critical field HC = 0.55 T. Experiments in hydrostatic pressure on UCo0.995Ru0.005Al and UCo0.9975Ru0.0025Al showed decay of ferromagnetism and increase of critical field. This behavior is similar to evolution of magnetism in UCoAl and URhAl in applied hydrostatic pressure. Keywords: UCoAl, URuAl, ferromagnetism, metamagnetism
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Optical response of magnetic materials
Wagenknecht, David ; Ostatnický, Tomáš (advisor) ; Antoš, Roman (referee)
David Wagenknecht: Abstract of a diploma thesis Optical response of magnetic materials, 2014 Magnetooptical properties of anisotropic semiconductors are studied to describe asymmetry of Ga1−xMnxAs, because theoretical calculations predict extraordinary behaviour of reflectivity. Analytical formulae to describe materials with non-diagonal permittivity are derived and they are used for the numerical calculations to describe the optical response of the samples available for the measurement. The transversal Kerr effect is calculated and it exhibits asymmetry in both rotation of the plane of polarization and ellipticity of circularly polarized light due to asymmetry in reflectivity. Moreover, longitudinal and polar magnetization are studied because of the influence on the observability of the phenomena. Results are not only used to discuss conditions, which must be satisfied to prove the asymmetry, but also the actual experimental setup is designed to prepare the measurement. 1
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