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Design of the apparatus for the measurement of the magnetic properties of the micro and nanostructures
Flajšman, Lukáš ; Dubroka, Adam (referee) ; Spousta, Jiří (advisor)
This bachelor's thesis deals with magneto-optic effects with special aim for magneto-optic Kerr effect. Presented description allows us to quantify magneto-optical observables on the basis of measuring the light intensity after the reflection from sample surface. Consequently, we use a simple physical model to unriddle the origin of the optical anisotropy induced by the external magnetic field. In the part, that deals with the design of an aparatus for measuring magneto-optical Kerr effect in longitudinal conformation, we provide necessary information to define a device capable of measuring magneto-optic observables in micro/nano scale. Last chapter i aimed to the achieved results on the thin Co films and on magnetic vortices with lateral dimensions of 1 m.
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Infrared magneto-spectroscopy of Bi2Te3 topological insulator
Mohelský, Ivan ; Výborný, Karel (referee) ; Orlita, Milan (advisor)
Tato práce se zabývá charakterizací topologického izolátoru Bi2Te3, materiálu s nevodivými stavy v objemu, ale jedním vodivým pásem na povrchu. Tento materiál je zkoumán již přes 60 let, ale i přes to není jeho objemová pásová struktura úplně objasněna, obzvláště charakter zakázaného pásu je stále předmětem diskuze. V této práci jsou prezentovány výsledky infračervené spektroskopie na Landauových hladinách v magnetickém poli až do 34 T, doplněné elipsometrickým měřením mimo magnetické pole. Výsledky těchto měření by měli pomoci vyjasnit některé vlastnosti zakázaného pásu. Pozorovaná optická odezva odpovídá polovodiči s přímým zakázaným pásem, ve kterém se nosiče náboje chovají jako Diracovské hmotné fermiony. Šířka zakázaného pásu za nízkých teplot byla určena jako Eg = (175±5) meV a samotný zakázaný pás se nachází mimo trigonální osu, tím pádem se v první Brillouinově zoně vyskytuje 6 krát nebo 12 krát.
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Optical study of magnetic anisotropy of ferromagnetic thin films
Hovořáková, Kristýna ; Schmoranzerová, Eva (advisor) ; Kašpar, Zdeněk (referee)
This work deals with the comparison of magneto-transport and magneto- optical methods for magnetic anisotropy measurements on a GaMnAs semicon- ductor. We performed measurements in the magnetotransport setup, and we determined the anisotropic constants from the study of the planar Hall effect. In the magneto-optical setup we studied the Voigt effect and from the obtained results we estimated the magnetic anisotropy of the sample. Our measurements have shown that both methods give analogous results. However, the use of the magnetooptical method has its limitations, which are reflected in the data processing itself. If the optical signal contains a contribution of non-magnetic origin, the analysis fails. At the end of the work we proposed a modified method of data analysis which managed to improve the obtained results. 1
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Investigation of magnetization dynamics in GaMnAs by ultrafast laser spectroscopy
Tesařová, Naďa ; Němec, Petr (advisor) ; Ferguson, Andrew (referee) ; Antoš, Roman (referee)
i Abstract: This doctoral thesis is dedicated to the study of magnetization dynamics in ferromagnetic semiconductor (Ga,Mn)As using magneto-optical (MO) spectroscopy methods. The character of the magnetization dynamics after the impact of the laser pulse was investigated under different experimental conditions in an extensive set of optimized (Ga,Mn)As samples with Mn doping ranging from 1.5% to 14%. The thorough analysis of the measured MO signal enabled us to develop a new method that can be used to determine the laser pulse-induced real-space magnetization trajectory without any numerical modelling. Moreover, the investigation of the measured MO signals allowed us to determine the basic micromagnetic properties of (Ga,Mn)As, such as the magnetic anisotropy, the Gilbert damping or the spin stiffness. In addition to this, we found out that the light-induced magnetization precession can be caused by three distinct mechanisms - the sample heating due to the energy transfer from the laser pulses, the angular momentum transfer from the circularly polarized photons, and the influence of the non-equilibrium hole polarization induced by the relativistic spin-orbit interaction. The first of these mechanisms is rather well known but the two remaining ones, which are the optical analogues of the spin-transfer torque...
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Infrared magneto-spectroscopy of Bi2Te3 topological insulator
Mohelský, Ivan ; Výborný, Karel (referee) ; Orlita, Milan (advisor)
Tato práce se zabývá charakterizací topologického izolátoru Bi2Te3, materiálu s nevodivými stavy v objemu, ale jedním vodivým pásem na povrchu. Tento materiál je zkoumán již přes 60 let, ale i přes to není jeho objemová pásová struktura úplně objasněna, obzvláště charakter zakázaného pásu je stále předmětem diskuze. V této práci jsou prezentovány výsledky infračervené spektroskopie na Landauových hladinách v magnetickém poli až do 34 T, doplněné elipsometrickým měřením mimo magnetické pole. Výsledky těchto měření by měli pomoci vyjasnit některé vlastnosti zakázaného pásu. Pozorovaná optická odezva odpovídá polovodiči s přímým zakázaným pásem, ve kterém se nosiče náboje chovají jako Diracovské hmotné fermiony. Šířka zakázaného pásu za nízkých teplot byla určena jako Eg = (175±5) meV a samotný zakázaný pás se nachází mimo trigonální osu, tím pádem se v první Brillouinově zoně vyskytuje 6 krát nebo 12 krát.
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Optical study of magnetic anisotropy of ferromagnetic thin films
Hovořáková, Kristýna ; Schmoranzerová, Eva (advisor) ; Kašpar, Zdeněk (referee)
This work deals with the comparison of magneto-transport and magneto- optical methods for magnetic anisotropy measurements on a GaMnAs semicon- ductor. We performed measurements in the magnetotransport setup, and we determined the anisotropic constants from the study of the planar Hall effect. In the magneto-optical setup we studied the Voigt effect and from the obtained results we estimated the magnetic anisotropy of the sample. Our measurements have shown that both methods give analogous results. However, the use of the magnetooptical method has its limitations, which are reflected in the data processing itself. If the optical signal contains a contribution of non-magnetic origin, the analysis fails. At the end of the work we proposed a modified method of data analysis which managed to improve the obtained results. 1
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Magneto-optical study of antiferromagnetic materials for spintronics
Kubaščík, Peter ; Němec, Petr (advisor) ; Výborný, Karel (referee)
The main goal of this thesis was to develop an experimental technique for investigation of ferromagnetic and antiferromagnetic materials using magneto-optical effects that are quadratic in magnetization. Using a prototype of 2-dimensional electromagnet, which enables to rotate magnetic field of constant magnitude in the sample plane, we were able to study spectral dependences and anisotropies of corresponding magneto-optical coefficients. In ferromagnetic semiconductor GaMnAs we revealed that the anisotropy of Voigt effect magneto-optical coefficient is strongly wavelength dependent - this coefficient can be both isotropic and anisotropic. Very strong anisotropy of this coefficient was observed for metallic FeRh in a ferromagnetic state. Finally, a new method that can be used to measure Voigt effect in antiferromagnetic state of FeRh was demonstrated.
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Magneto-optical characterization of spintronic materials
Wohlrath, Vladislav ; Němec, Petr (advisor) ; Olejník, Kamil (referee)
This work deals with magneto-optical measurements using a recently built prototype of a two- dimensional electromagnet. In the first stage, an experimental setup for magneto-optical measurements was constructed, which enables to study Voigt effect and magnetic linear dichroism. In the second stage, this setup was tested by measuring hysteresis loops in a sample of ferromagnetic semiconductor GaMnAs. In the final stage, we performed a new type of magneto- optical experiments, which fully exploits the two-dimensional control of the magnetic field generated in the electromagnet.
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Investigation of magnetization dynamics in GaMnAs by ultrafast laser spectroscopy
Tesařová, Naďa ; Němec, Petr (advisor) ; Ferguson, Andrew (referee) ; Antoš, Roman (referee)
i Abstract: This doctoral thesis is dedicated to the study of magnetization dynamics in ferromagnetic semiconductor (Ga,Mn)As using magneto-optical (MO) spectroscopy methods. The character of the magnetization dynamics after the impact of the laser pulse was investigated under different experimental conditions in an extensive set of optimized (Ga,Mn)As samples with Mn doping ranging from 1.5% to 14%. The thorough analysis of the measured MO signal enabled us to develop a new method that can be used to determine the laser pulse-induced real-space magnetization trajectory without any numerical modelling. Moreover, the investigation of the measured MO signals allowed us to determine the basic micromagnetic properties of (Ga,Mn)As, such as the magnetic anisotropy, the Gilbert damping or the spin stiffness. In addition to this, we found out that the light-induced magnetization precession can be caused by three distinct mechanisms - the sample heating due to the energy transfer from the laser pulses, the angular momentum transfer from the circularly polarized photons, and the influence of the non-equilibrium hole polarization induced by the relativistic spin-orbit interaction. The first of these mechanisms is rather well known but the two remaining ones, which are the optical analogues of the spin-transfer torque...
|
|
|
Design of the apparatus for the measurement of the magnetic properties of the micro and nanostructures
Flajšman, Lukáš ; Dubroka, Adam (referee) ; Spousta, Jiří (advisor)
This bachelor's thesis deals with magneto-optic effects with special aim for magneto-optic Kerr effect. Presented description allows us to quantify magneto-optical observables on the basis of measuring the light intensity after the reflection from sample surface. Consequently, we use a simple physical model to unriddle the origin of the optical anisotropy induced by the external magnetic field. In the part, that deals with the design of an aparatus for measuring magneto-optical Kerr effect in longitudinal conformation, we provide necessary information to define a device capable of measuring magneto-optic observables in micro/nano scale. Last chapter i aimed to the achieved results on the thin Co films and on magnetic vortices with lateral dimensions of 1 m.
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