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Ultrafast laser spectroscopy of antiferromagnets
Saidl, Vít ; Němec, Petr (advisor) ; Kužel, Petr (referee) ; Hamrle, Jaroslav (referee)
This work is dedicated to the study of two antiferromagnetic materials that are suitable for use in spintronic devices. In series of FeRh samples we studied the transition temperature between the antiferromagnetic and ferromagnetic phases. We developed a method based on material optical response for a quick determination of this temperature, which enabled us to study with a spatial resolution of 1 μm a magnetic inhomogeneity of prepared samples.We also developed a method for a determination of the Néel temperature and the magnetization easy axis position in thin films prepared from compensated antiferromagnetic metal. We successfully applied this method on an uniaxial sample of CuMnAs and we discussed its applicability for a research of samples with a biaxial magnetic anisotropy.
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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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Nanostructures and Materials for Antiferromagnetic Spintronics
Reichlová, Helena ; Novák, Vít (advisor) ; Ferguson, Andrew (referee) ; Kunc, Jan (referee)
This thesis is focused on two open problems of antiferromagnetic (AFM) spintronics: manipulation of AFM coupled moments and development of new materials combining AFM and semiconductor properties. We present three particular methods enabling AFM moments manipulation. The rst method, based on the exchange spring effect in an AFM/FM double layer, strongly de- pends on the AFM layer thickness and temperature. We systematically vary these two parameters and identify the conditions when AFM moments can be manip- ulated. By the second method, cooling an AFM in a magnetic eld through the critical temperature, we prove the concept of a fully AFM-based (containing no FM) spintronic device. The last studied method is based on current induced effects in nanostructures containing an AFM. By systematic study of samples with and without AFM we demonstrate the ability of AFM moments to absorb a current induced torque. Relying neither on a FM nor on cooling in magnetic eld, this method represents an elegant way of AFM moments manipulation. In the second experimental part new materials for AFM spintronics are discussed, and one representative example, CuMnAs, is studied in detail. Characterization of bulk and epitaxial CuMnAs is presented and rst spintronic functionality is shown. Powered by TCPDF (www.tcpdf.org)
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Studium precese magnetizace v materiálech a strukturách pro spintroniku
Kašpar, Zdeněk ; Olejník, Kamil (advisor) ; Veis, Martin (referee)
In this thesis we studied precession mechanism in ferromagnetic thin film half-metal NiMnSb. We measured magnetization oscillations using optical pump and probe experiment at temperatures between 15 and 200 K and we evaluated the magnetic anisotropy fields, spin stiffness and Gilbert damping. New setup for ferromagnetic resonance measurement was built utilizing vector network analyser. With this setup we measured FMR at temperatures between 300 and 75 K. We evaluated the same parameters from FMR experiments as from the optical one. We found very good agreement in results obtained by the two methods. Powered by TCPDF (www.tcpdf.org)
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Nanostructures and Materials for Antiferromagnetic Spintronics
Reichlová, Helena ; Novák, Vít (advisor)
This thesis is focused on two open problems of antiferromagnetic (AFM) spintronics: manipulation of AFM coupled moments and development of new materials combining AFM and semiconductor properties. We present three particular methods enabling AFM moments manipulation. The rst method, based on the exchange spring effect in an AFM/FM double layer, strongly de- pends on the AFM layer thickness and temperature. We systematically vary these two parameters and identify the conditions when AFM moments can be manip- ulated. By the second method, cooling an AFM in a magnetic eld through the critical temperature, we prove the concept of a fully AFM-based (containing no FM) spintronic device. The last studied method is based on current induced effects in nanostructures containing an AFM. By systematic study of samples with and without AFM we demonstrate the ability of AFM moments to absorb a current induced torque. Relying neither on a FM nor on cooling in magnetic eld, this method represents an elegant way of AFM moments manipulation. In the second experimental part new materials for AFM spintronics are discussed, and one representative example, CuMnAs, is studied in detail. Characterization of bulk and epitaxial CuMnAs is presented and rst spintronic functionality is shown. Powered by TCPDF (www.tcpdf.org)
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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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