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Magnetic nanostructures with application potential
Bittová, Barbara ; Kalbáčová Vejpravová, Jana (advisor)
Title: Magnetic structures with application potential Author: Bc. Barbara Bittová Department: Department of condensed matter physics Supervisor: RNDr. Jana Poltierová Vejpravová Ph.D. Supervisor's e-mail address: jana@mag.cuni.cz Abstract: The thesis is mainly focused on the investigation of macroscopic and microscopic magnetic properties of selected nanomaterials containing cobalt and iron, and also the capability of our new device, scanning probe microscope Multimode V by Veeco, to directly visualise morphology and magnetic structure of these samples (Magnetic Force Miscroscopy, MFM). Investigated materials, such as CoFe2O4 nanoparticles and SiO2_Co_Si(111) thin films and multilayers are in general promising materials in many fields. In the medicine, the nanoparticles are used as the drug targets or contrast agents whereas in electronics, the (nano)granular thin films are the starting point in fabrication of high density storage media. The macroscopic magnetic properties of our samples are discusses in a view of superparamagnetic phenomena. The interactions in systems of nanoparticles are presented theoretically within the up-to date knowledge and also experimentally by demonstrating the behavior of the strongly-interacting, super-spin-glass system. The thin films are studied in term of their granular...
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Magnetism in transition metal oxides
Burianová, Simona ; Kalbáčová Vejpravová, Jana (advisor)
Title: Magnetism in transition metal oxides Author: Simona Burianová Department: Department of Condensed Matter Physics Supervisor: RNDr. Jana Poltierová Vejpravová, Ph.D. Supervisor's e-mail address: jana@mag.mff.cuni.cz Abstract: The CoFe2O4 nanocrystals are highly attractive due to their magnetic properties - large coercivity (up to 2 T at low temperatures) with moderate saturation magnetization (80 A.m2 .kg-1 ), remarkable chemical stability and mechanical hardness. Upon RE doping, a significant change of the properties is expected. This thesis is focused on investigation of Co1- xLaxFe2O4, x = 0.05 - 0.5 and CoLaxFe2-x O4 x = 0.05 - 0.2 nanoparticles prepared by sol-gel and microemulsion method, respectively, with varying particle size according to the final heat treatment. In the former case, the particles were embedded in amorphous SiO2 matrix, while in the latter case, the samples were matrix-free. The samples were characterized using X-ray diffraction and Mössbauer spectroscopy. Measurements of the temperature dependence of the ZFC-FC magnetization revealed that the blocking temperature is above the room temperature. The values of coercivity and saturation magnetization strongly depend on particles size determined by method of preparation. The higher coercivity values of about 2 T at 10 K show the...
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Ultrapure metallic materials
Prachařová, Marcela ; Kalbáčová Vejpravová, Jana (advisor)
Title: Ultrapure metallic materials Author: Bc. Marcela Janatová Department: Department of Condensed Matter Physics Supervisor: RNDr. Jana Poltierová Vejpravová, Ph.D. Supervisor's e-mail address: jana@mag.mff.cuni.cz Abstract This thesis deals with crystal structure and magnetic properties of RCr2Si2 (R = Pr, Tb, Er) and RCr2Si2C (R = La, Ce, Pr, Nd) compounds. All prepared samples were characterized by powder X-ray diffraction and investigated by specific-heat, magne- tization and AC-susceptibility measurements in the temperature range 2-900 K and in magnetic fields up to 9 T. The results suggest non-trivial magnetic ordering of the Cr sublattice in all studied compounds, accompanied with ferromagnetic ordering of the Pr and Nd magnetic moments below the Curie temperature of 30 and 21 K in PrCr2Si2C and NdCr2Si2C, respectively, and possible metamagnetism in CeCr2Si2C. For RCr2Si2C compounds, the experimental evidence of Cr magnetism is corrobora- ted by results of extended first-principles calculations based on the density functional theory. Keywords: RCr2Si2 compounds; RCr2Si2C compounds; Magnetic ordering; Heat ca- pacity; Magnetization 1
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Nanostructures of magnetoresponsive transition metal oxides
Řezníčková, Alice ; Kalbáčová Vejpravová, Jana (advisor) ; Mihalik, Matúš (referee) ; Svoboda, Pavel (referee)
The thesis is focused on investigation of structural and magnetic properties of nanocomposites consisting of transition-oxide-based nanoparticles (NPs; CoFe2O4 and Fe2O3) embedded in dielectric matrices (SiO2, CeO2, TiO2, ZrO2, Al2O3). The nanocomposites were studied by broad range of complementary techniques (X-ray diffraction, electron microscopy, energy dispersive x-ray analysis, Mössbauer Spectroscopy and Magnetic measurements). Among them, analysis of the distributions of the NP magnetic moments and blocking temperatures was identified as a powerful tool for characterization of NP changes due to mutual interactions, surface modifications and embedding into the functional matrices. The effect of structural and spin order of the individual NPs on the volume magnetic response is also addressed. The obtained results imply new strategies for design of efficient heat nanogenerators and catalysts.
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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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Ultrapure metallic materials
Prachařová, Marcela ; Kalbáčová Vejpravová, Jana (advisor)
Title: Ultrapure metallic materials Author: Bc. Marcela Janatová Department: Department of Condensed Matter Physics Supervisor: RNDr. Jana Poltierová Vejpravová, Ph.D. Supervisor's e-mail address: jana@mag.mff.cuni.cz Abstract This thesis deals with crystal structure and magnetic properties of RCr2Si2 (R = Pr, Tb, Er) and RCr2Si2C (R = La, Ce, Pr, Nd) compounds. All prepared samples were characterized by powder X-ray diffraction and investigated by specific-heat, magne- tization and AC-susceptibility measurements in the temperature range 2-900 K and in magnetic fields up to 9 T. The results suggest non-trivial magnetic ordering of the Cr sublattice in all studied compounds, accompanied with ferromagnetic ordering of the Pr and Nd magnetic moments below the Curie temperature of 30 and 21 K in PrCr2Si2C and NdCr2Si2C, respectively, and possible metamagnetism in CeCr2Si2C. For RCr2Si2C compounds, the experimental evidence of Cr magnetism is corrobora- ted by results of extended first-principles calculations based on the density functional theory. Keywords: RCr2Si2 compounds; RCr2Si2C compounds; Magnetic ordering; Heat ca- pacity; Magnetization 1
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Structure and magnetic interactions in nanomaterials with application potential
Pacáková, Barbara ; Kalbáčová Vejpravová, Jana (advisor) ; Jirásková, Yvona (referee) ; Svoboda, Pavel (referee)
The thesis is focused on the physics of magnetic nanoparticles (NPs), starting from the solution of magnetic structure, internal alignment within the single particle and role of interactions and particle structure in magnetic response of systems of the NPs. Moreover, the macroscopic arrangement of the NPs and its effect on the properties of system containing the NPs are discussed. The work brings several new results and concepts, such as the solution of magnetic structure of the ε-Fe2O3 phase, methods of proper detection and description of magnetic metal catalyst in carbon nanotubes and role of the NP arrangement and their effect on graphene placed on the top of substrates decorated with the NPs. 1
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Magnetic nanostructures with application potential
Bittová, Barbara ; Kalbáčová Vejpravová, Jana (advisor)
Title: Magnetic structures with application potential Author: Bc. Barbara Bittová Department: Department of condensed matter physics Supervisor: RNDr. Jana Poltierová Vejpravová Ph.D. Supervisor's e-mail address: jana@mag.cuni.cz Abstract: The thesis is mainly focused on the investigation of macroscopic and microscopic magnetic properties of selected nanomaterials containing cobalt and iron, and also the capability of our new device, scanning probe microscope Multimode V by Veeco, to directly visualise morphology and magnetic structure of these samples (Magnetic Force Miscroscopy, MFM). Investigated materials, such as CoFe2O4 nanoparticles and SiO2_Co_Si(111) thin films and multilayers are in general promising materials in many fields. In the medicine, the nanoparticles are used as the drug targets or contrast agents whereas in electronics, the (nano)granular thin films are the starting point in fabrication of high density storage media. The macroscopic magnetic properties of our samples are discusses in a view of superparamagnetic phenomena. The interactions in systems of nanoparticles are presented theoretically within the up-to date knowledge and also experimentally by demonstrating the behavior of the strongly-interacting, super-spin-glass system. The thin films are studied in term of their granular...
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Magnetism in transition metal oxides
Burianová, Simona ; Kalbáčová Vejpravová, Jana (advisor)
Title: Magnetism in transition metal oxides Author: Simona Burianová Department: Department of Condensed Matter Physics Supervisor: RNDr. Jana Poltierová Vejpravová, Ph.D. Supervisor's e-mail address: jana@mag.mff.cuni.cz Abstract: The CoFe2O4 nanocrystals are highly attractive due to their magnetic properties - large coercivity (up to 2 T at low temperatures) with moderate saturation magnetization (80 A.m2 .kg-1 ), remarkable chemical stability and mechanical hardness. Upon RE doping, a significant change of the properties is expected. This thesis is focused on investigation of Co1- xLaxFe2O4, x = 0.05 - 0.5 and CoLaxFe2-x O4 x = 0.05 - 0.2 nanoparticles prepared by sol-gel and microemulsion method, respectively, with varying particle size according to the final heat treatment. In the former case, the particles were embedded in amorphous SiO2 matrix, while in the latter case, the samples were matrix-free. The samples were characterized using X-ray diffraction and Mössbauer spectroscopy. Measurements of the temperature dependence of the ZFC-FC magnetization revealed that the blocking temperature is above the room temperature. The values of coercivity and saturation magnetization strongly depend on particles size determined by method of preparation. The higher coercivity values of about 2 T at 10 K show the...
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Structure and magnetism of transition metal-based nanoparticles
Mantlíková, Alice ; Kalbáčová Vejpravová, Jana (advisor) ; Prchal, Jiří (referee)
The aim of the work is characterization of structure and magnetic properties of various CoFe2O4/SiO2 nanocomposites. Emphasis was put on the corelation of the magnetic properties with particle size (samples with different annealing temperature) and with strenght of the interparticle interactions (samples with different Fe/Si ratio or without silica matrix). Structure properties of all samples were determinated by powder x-ray diffraction, scanning and transmission electron microscopy. Magnetic properties were determinated by standard (temperature dependence of magnetization, magnetization isotherms) and advanced (a.c. susceptibility, memory effects) magnetic measurements. A sharp increase of the values of blocking temperature and coercivity with increase of strenght of the interparticle interactions and with increase of particle size was observed. Particle size determines the maximum value of coercivity and blocking temperature and strengh of the interparticle interactions shift this values in the interval determined by particle size.
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