|
|
Ultrafast laser-induced control of magnetic materials
Opršal, Jakub ; Wojewoda, Ondřej (referee) ; Arregi Uribeetxebarria, Jon Ander (advisor)
Magnetické materiály jsou ve velkém používány pro ukládání dat, která jsou zapisována ve formě bitů pomocí externího magnetického pole. Dlouho se věřilo, že doba potřebná pro změnu magnetizace je v řádu desítek až stovek pikosekund. Revoluční experiment v roce 1996 položil základ pro nový obor ultrarychlého ovládání magnetických materiálů, řádově zkracující čas potřebný pro změnu magnetizace. Mimo jiné ukázal, že magnetizace materiálu může být ovlivněna i světelnými pulzy. V této práci jsme replikovali fundamentální, laserem indukované experimenty ve ferromagnetických a ferrimagnetických materiálech. Postavili jsme optickou sestavu schopnou provádět tyto experimenty pro různé polarizace světla. Tato variabilita umožňuje rozlišit různé mechanismy a jevy, které se vyskytují při ultrarychlém ovládání magnetizace magnetických materiálů.
|
|
|
Measurement of thin films properties by imaging spectroscopy and magnetooptical Kerr effect
Plšek, Radek ; Navrátil, Karel (referee) ; Spousta, Jiří (advisor)
This thesis is divided into three main sections that deal with optical and magnetic thin films properties and their measurements techniques. Principles of the spectroscopic reflectometry and measurements of optical properties are described in the first part. Results of imaging reflectometry are most important. This technique is based on in situ monitoring of optical properties of SiO2 thin films during etching over the area cca 10 × 13 mm2. In next section magnetic properties of thin films and new apparatus built on the Institute of Physical Engineering of BUT are shown. Magnetic properties were observed by longitudinal magneto-optical Kerr effect. The construction of the device is based on a light beam with rectilinear polarization reflected from magnetic material with turned polarization. For investigation of local magnetic properties of microstructures a microscope objective focusing laser beam on the sample is used. The last part of the thesis is aimed on improving of a spin valve structure Co/Cu/NiFe. This work was done within the frame of the Erasmus project in Laboratoire Louis Néel in Grenoble. The goal was to achieve the value of GMR (Giant Magnetoresistance) as high as possible by changing of deposition parameters. This value describes the rate of resistances in different mutual directions of magnetization in trilayers.
|
|
|
Ultrafast laser-induced control of magnetic materials
Opršal, Jakub ; Wojewoda, Ondřej (referee) ; Arregi Uribeetxebarria, Jon Ander (advisor)
Magnetické materiály jsou ve velkém používány pro ukládání dat, která jsou zapisována ve formě bitů pomocí externího magnetického pole. Dlouho se věřilo, že doba potřebná pro změnu magnetizace je v řádu desítek až stovek pikosekund. Revoluční experiment v roce 1996 položil základ pro nový obor ultrarychlého ovládání magnetických materiálů, řádově zkracující čas potřebný pro změnu magnetizace. Mimo jiné ukázal, že magnetizace materiálu může být ovlivněna i světelnými pulzy. V této práci jsme replikovali fundamentální, laserem indukované experimenty ve ferromagnetických a ferrimagnetických materiálech. Postavili jsme optickou sestavu schopnou provádět tyto experimenty pro různé polarizace světla. Tato variabilita umožňuje rozlišit různé mechanismy a jevy, které se vyskytují při ultrarychlém ovládání magnetizace magnetických materiálů.
|
|
|
Studium fyzikálních vlastostí magnetických oxidů spektroskopickými metodami
Zahradník, Martin ; Veis, Martin (advisor) ; Kouřil, Karel (referee)
Two groups of magnetic oxides were investigated in this thesis. Thin films of La2/3Sr1/3MnO3 (LSMO) deposited by pulsed laser deposition (PLD) on SrTiO3 (STO) substrates were characterized by polar and longitudinal magneto-optical (MO) Kerr spectroscopy. Experimental results were compared to theoretical calculations based on the transfer matrix formalism. A very good agreement between experimental and theoretical data revealed high magnetic ordering down to 5 nm of film thickness as well as a mechanism of suppression of double exchange interaction near the LSMO/STO interface. Magnetically doped Ce1-xCoxO2-δ films deposited by PLD on MgO (x = 0.05 and 0.10) and oxidized Si (x = 0.20) substrates were studied by combination of spectroscopic ellipsometry and MO Faraday and Kerr spectroscopy. Both diagonal and off-diagonal permittivity tensor components were obtained and verified by theoretical calculations confronted with experimental data. Diagonal spectra revealed two optical transitions from oxygen to cerium states. Off-diagonal spectra revealed two paramagnetic transitions involving cobalt ions. An essential influence of cobalt doping on the resulting ferromagnetic properties of CeO2 was observed.
|
|
|
Vliv pnutí na magnetooptické vlasnosti La2/3Sr1/3MnO3
Maleček, Tomáš ; Veis, Martin (advisor) ; Verhagen, Timotheus Guillaume Albertus (referee)
The influence of epitaxial strain on La2/3Sr1/3MnO3 (LSMO) thin films has been studied by magneto-optical spectroscopy. The investigated samples have been grown by pulsed laser deposition on four different substrates with varying degree of compressive and tensile strain. The spectra of the magneto-optical Kerr effect (MOKE) have been measured. Deterioration of magnetic properties with increasing epitaxial strain has been observed. The off-diagonal elements of the permittivity tensor, numerically calculated from the MOKE and spectroscopic ellipsometry measurements, confirmed two already reported electronic transitions. A third transition at around 4.3 eV has been observed on samples grown under compressive strain. The dependence of the Kerr rotation spectra on temperature has been measured for all four samples. The Curie temperatures have been estimated for all samples with the exception of LSMO grown on LaAlO3 which undergoes a spin reorientation transition at 200 K. The low temperature measurements on the compressively strained samples showed amplification of the third transition supporting the claim of it being paramagnetic. Also observed was a change in the spectra of the Kerr rotation of the sample grown on SrTiO3 which undergoes a structural transition at 105 K, and, therefore, changes the epitaxial strain.
|
|
|
Studium fyzikálních vlastností magnetických oxidů spektroskopickými metodami
Zahradník, Martin ; Veis, Martin (advisor)
Two groups of magnetic oxides were investigated in this thesis. Thin films of La2/3Sr1/3MnO3 (LSMO) deposited by pulsed laser deposition (PLD) on SrTiO3 (STO) substrates were characterized by polar and longitudinal magneto-optical (MO) Kerr spectroscopy. Experimental results were compared to theoretical calculations based on the transfer matrix formalism. A very good agreement between experimental and theoretical data revealed high magnetic ordering down to 5 nm of film thickness as well as a mechanism of suppression of double exchange interaction near the LSMO/STO interface. Magnetically doped Ce1-xCoxO2-δ films deposited by PLD on MgO (x = 0.05 and 0.10) and oxidized Si (x = 0.20) substrates were studied by combination of spectroscopic ellipsometry and MO Faraday and Kerr spectroscopy. Both diagonal and off-diagonal permittivity tensor components were obtained and verified by theoretical calculations confronted with experimental data. Diagonal spectra revealed two optical transitions from oxygen to cerium states. Off-diagonal spectra revealed two paramagnetic transitions involving cobalt ions. An essential influence of cobalt doping on the resulting ferromagnetic properties of CeO2 was observed.
|
|
|
Vliv pnutí na magnetooptické vlasnosti La2/3Sr1/3MnO3
Maleček, Tomáš ; Veis, Martin (advisor) ; Verhagen, Timotheus Guillaume Albertus (referee)
The influence of epitaxial strain on La2/3Sr1/3MnO3 (LSMO) thin films has been studied by magneto-optical spectroscopy. The investigated samples have been grown by pulsed laser deposition on four different substrates with varying degree of compressive and tensile strain. The spectra of the magneto-optical Kerr effect (MOKE) have been measured. Deterioration of magnetic properties with increasing epitaxial strain has been observed. The off-diagonal elements of the permittivity tensor, numerically calculated from the MOKE and spectroscopic ellipsometry measurements, confirmed two already reported electronic transitions. A third transition at around 4.3 eV has been observed on samples grown under compressive strain. The dependence of the Kerr rotation spectra on temperature has been measured for all four samples. The Curie temperatures have been estimated for all samples with the exception of LSMO grown on LaAlO3 which undergoes a spin reorientation transition at 200 K. The low temperature measurements on the compressively strained samples showed amplification of the third transition supporting the claim of it being paramagnetic. Also observed was a change in the spectra of the Kerr rotation of the sample grown on SrTiO3 which undergoes a structural transition at 105 K, and, therefore, changes the epitaxial strain.
|
|
|
Dynamic control of magnetization for spintronic applications studied by magneto-optical methods
Zahradník, Martin ; Veis, Martin (advisor) ; Herranz, Gervasi (referee) ; Legut, Dominik (referee)
Two important mechanisms in preparation of ultrathin films of magnetic oxides were systematically investigated in this work. First, influence of epitaxial strain on resulting magneto-optical properties of La2/3Sr1/3MnO3 (LSMO) ultrathin films was studied. The investigated films were grown by pulsed laser deposition on four different substrates, providing a broad range of induced epitaxial strains. Magnetic properties were found to deteriorate with increasing value of the epitaxial strain, as expected due to the unit cell distortion increasingly deviating from the bulk and effect of the magnetically inert layer. A combination of spectroscopic ellipsometry and magneto-optical Kerr effect spectroscopy was used to determine spectra of the diagonal and off-diagonal elements of permittivity tensor. The off-diagonal elements confirmed presence of two previously reported electronic transitions in spectra of all films. Moreover, they revealed another electronic transition around 4.3 eV only in spectra of films grown under compressive strain. We proposed classification of this transition as crystal field paramagnetic Mn t2g → eg transition, which was further supported by ab initio calculations. A key role of strain in controlling electronic structure of ultrathin perovskite films was demonstrated. Dynamic application of...
|
|
|
Physics of interfaces in magnetic nano structures
Ohnoutek, Lukáš ; Veis, Martin (advisor) ; Urbánek, Michal (referee)
Modification of interfaces in nanostructures can significantly influence their overall properties. Magneto-optical spectroscopy and spectroscopic ellipsometry are ideal for studying these phenomena thanks to their in-depth sensitivity and contactless measurements. Two methods of nonreversible modification of magnetic properties, especially the magnetic anisotropy, are investigated. The measured spectral dependence of magneto-optical Kerr effect is compared to a theoretical calculation in order to determine the profile of the samples for different levels and methods of modification. In addition to this, ellipsometric measurements are performed on a device whose optical properties change by voltage application.
|
|
|
Studium fyzikálních vlastností magnetických oxidů spektroskopickými metodami
Zahradník, Martin ; Veis, Martin (advisor)
Two groups of magnetic oxides were investigated in this thesis. Thin films of La2/3Sr1/3MnO3 (LSMO) deposited by pulsed laser deposition (PLD) on SrTiO3 (STO) substrates were characterized by polar and longitudinal magneto-optical (MO) Kerr spectroscopy. Experimental results were compared to theoretical calculations based on the transfer matrix formalism. A very good agreement between experimental and theoretical data revealed high magnetic ordering down to 5 nm of film thickness as well as a mechanism of suppression of double exchange interaction near the LSMO/STO interface. Magnetically doped Ce1-xCoxO2-δ films deposited by PLD on MgO (x = 0.05 and 0.10) and oxidized Si (x = 0.20) substrates were studied by combination of spectroscopic ellipsometry and MO Faraday and Kerr spectroscopy. Both diagonal and off-diagonal permittivity tensor components were obtained and verified by theoretical calculations confronted with experimental data. Diagonal spectra revealed two optical transitions from oxygen to cerium states. Off-diagonal spectra revealed two paramagnetic transitions involving cobalt ions. An essential influence of cobalt doping on the resulting ferromagnetic properties of CeO2 was observed.
|
guest ::
