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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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Light propagation in magnetic materials
Wagenknecht, David ; Ostatnický, Tomáš (advisor) ; Veis, Martin (referee)
Transparent magnetic materials, among the others semiconductors, have recently come to the focus of interest in both basic and applied research because they have great potential in optical applications and they can be used in optical spectroscopy to investigate fundamental physical phenomena. The theoretical calculations introduce that these materials have some extraordinary properties like asymmetric reflectance when light impact the sample from the opposite angles. In this bachelor thesis, transfer matrix formalism is derived based on Maxwell equations, taking into account special form of effective permittivity. The reflection coefficient for one layer demonstrates, that the asymmetric reflectance appears for transversal- magnetic polarization of light and transversal magnetization in the studied material. The derived formulae are used to calculate the difference in reflectivities for the waves impacting the structure from opposite angles. Ga1−xMnxAs with different concentrations of manganese is assumed to be the essential transparent magnetic layer in the sample. 1
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Dynamics of spin polarization in semiconductors
Janda, Tomáš
In this work we study ultrafast laser-induced magnetization dynamics in samples of ferromagnetic semiconductor Ga1−xMnxAs with a nominal concentration of Mn within the range of x = 0,015-0,14. To get information about magnetization movement we use magneto-optic phenomena PKE and MLD in a time-resolved pump & probe experiment. Thorough analysis of the measured magneto-optical signal allows us to disentangle contributions due to angular movement of magnetization and due to demagnetization and to reconstruct 3D motion of magnetization vector without any numerical modeling. First we explain the basis of this experimental method and we demonstrate its utilization on the measured data. After that we study angular movement of magnetization vector and its dependence on the external magnetic field, excitation intensity and Mn concentration. The pump pulse helicity dependent and independent dynamics were treated separately. In the case of demagnetization we have been able to observe not only its intensity and Mn doping dependence but also the magnetic field dependence, which has not been reported so far in the literature.
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Optical response of magnetic materials
Wagenknecht, David ; Ostatnický, Tomáš (advisor)
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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Dynamics of spin polarization in ferromagnetic semiconductors
Šubrt, Jiří
This work was devoted to the measurement of magnetooptical effects in ferromagnetic semiconductors. We analyzed in detail the measurement technique based on a photoelastic modulator and we constructed an experimental setup that enables to measure the spectra of magnetic circular dichroism (MCD), magnetic circular birefringence (MCB), magnetic linear dichroism (MLD), and magnetic linear birefringence (MLB). This setup was used for the measurement of magnetooptical spectra of several samples of ferromagnetic semiconductors (Ga,Mn)As and (Ga,Mn)(As,P).
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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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Optical response of magnetic materials
Wagenknecht, David ; Ostatnický, Tomáš (advisor)
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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Investigation of anizotropic magnetorezistence of ferromagnetic semiconductor GaMnAs
Kašpar, Zdeněk ; Němec, Petr (advisor) ; Svoboda, Štěpán (referee)
This thesis is devoted to the measurement of the anisotropic magnetoresistance (AMR) on a series of samples that were prepared by the molecular beam epitaxy (MBE). The measurements were taken during a rotation of a magnetic field in the sample plane using a vector magnet in a cryostat, which allows to change the working temperature from 1.5 to 300 Kelvin. The dependences of anisotropic magnetotransport parameters on the Mn concentration were evaluated from the measured data. Moreover, the temperature dependence of these parameters was also studied. Identification of experimental artifact in the measured data enabled us to reveal a significant influence of the hysteresis of the magnets on the measurements. Finally, by measuring in weak magnetic fields we studied the magnetic anisotropy of the samples. Powered by TCPDF (www.tcpdf.org)
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