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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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Spin dynamics in GaAs-based semiconductor structures
Schmoranzerová, Eva ; Němec, Petr (advisor) ; Postava, Kamil (referee) ; Kužel, Petr (referee)
This work is dedicated to the study of spin dynamics in systems based on the semiconductor gallium arsenide (GaAs) that are suitable for use in spintronic devices. We explored two types of model structures using experimental methods of ultrafast laser spectroscopy and transport measurements. In the ferromagnetic semiconductor (Ga,Mn)As, we investigated laser-induced magnetization precession. We found out that transfer of both energy and angular momentum from the circularly polarized laser light can trigger magnetization precession, the latter one being identified as a new phenomenon, the "optical spin transfer torque". Furthermore, we demonstrate the possibility to control the energy-transfer-induced magnetization dynamics both optically and electrically using piezo-stressing. When dealing with purely non-magnetic structures for spintronics, we studied the Spin-Injection Hall Effect (SIHE) in GaAs/AlGaAs heterostructures with a special type of spin- orbit (SO) coupling that are lithographically patterned to create nanodevices. We managed to observe precession of the electron spin in the SO field directly in the space domain by extending the original detection method. This finding, together with the direct detection of a pure spin current, helped to propose a working spin Hall effect transistor.
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Dynamics of spin polarization in semiconductors
Janda, Tomáš ; Němec, Petr (advisor) ; Olejník, Kamil (referee)
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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Magnetic multilayers for spintronics applications
Vaňatka, Marek ; Dvořák, Petr (referee) ; Urbánek, Michal (advisor)
Magnetic multilayers have applications as magnetic field sensors or magnetic memory cells. Mastering the methods of fabrication and characterization of the structures such as spin valve or magnetic tunnel junction is an important step towards more complicated spintronics devices. This work summarizes basic theory of magnetism, magnetotransport properties, and it describes basic applications of magnetic multilayers. The experimental part of this work deals with the sample preparation by ion beam sputtering (IBS), ion beam assisted deposition (IBAD), and characterization of prepared multilayers by measuring anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), or tunnel magnetoresistance (TMR).
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