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Modeling and study of quasi-two-dimensional magnetic materials
Priessnitz, Jan ; Baláž, Pavel (advisor) ; Legut, Dominik (referee)
Dzyaloshinskii-Moriya interaction (DMI) is a type of exchange interaction found in non-centrosymmetric structures. It favors spin canting, and it is an important mechanism for stabilizing non-collinear magnetic structures, such as skyrmions, which are promising candidates for applications in spintronics. Furthermore, DMI plays a significant role in multiferroics and can support magnetoelectricity. Both phenomena are often observed in layered materials. This thesis explores, through numerical simulations, the effect of out-of-plane DMI on magnetic ordering in two-dimensional triangular lattices. It uses the classical Heisenberg model together with Markov Chain Monte Carlo and spin dynamics simulation methods. Apart from DMI, the Hamiltonian includes ferromagnetic exchange interaction between nearest neighbours and interaction with external magnetic field. In the first part, the zero-temperature properties of the system are computed for various DMI strengths and external magnetic fields, and a phase diagram is constructed. Three magnetic phases are observed: ferromagnetic, antiferromagnetic cycloidal, and conical - a mixture of the former two. The second part focuses on finite-temperature properties, starting with specific heat capacity, magnetization, and magnetic susceptibility. DMI does not affect the...
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Electronic structure and magnetic properties of the materials with strong electron-electron correlation
Kozub, Agnieszka Lidia ; Shick, Alexander (advisor) ; Legut, Dominik (referee) ; Minár, Ján (referee)
In this thesis, we summarize the material-specific theories of strongly correlated systems and apply them to selected materials. We describe and apply the corre- lated band theory methods: the local density approximation plus Coulomb U, and the density functional theory plus exact diagonalization of single impurity An- derson model. First, we investigate the systems containing impurity atoms: cobalt impurity located in the bulk copper and samarium, and neodymium adatoms on the surface of graphene. We present the spectral densities and study the magnetism of those compounds. Afterwards, we analyze three Np-based compounds: NpPt2In7, Np2Ni17 and NpBC. For all three compounds we analyze the spin, orbital and to- tal magnetic moments and the total density of states, as well as its projections for selected orbitals and spins. Moreover, for NpPt2In7 and NpBC we perform the to- tal energy analysis between different magnetic moment arrangements on the Np atoms.
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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...
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Electronic structure and magnetic properties of the materials with strong electron-electron correlation
Kozub, Agnieszka Lidia ; Shick, Alexander (advisor) ; Legut, Dominik (referee) ; Minár, Ján (referee)
In this thesis, we summarize the material-specific theories of strongly correlated systems and apply them to selected materials. We describe and apply the corre- lated band theory methods: the local density approximation plus Coulomb U, and the density functional theory plus exact diagonalization of single impurity An- derson model. First, we investigate the systems containing impurity atoms: cobalt impurity located in the bulk copper and samarium, and neodymium adatoms on the surface of graphene. We present the spectral densities and study the magnetism of those compounds. Afterwards, we analyze three Np-based compounds: NpPt2In7, Np2Ni17 and NpBC. For all three compounds we analyze the spin, orbital and to- tal magnetic moments and the total density of states, as well as its projections for selected orbitals and spins. Moreover, for NpPt2In7 and NpBC we perform the to- tal energy analysis between different magnetic moment arrangements on the Np atoms.
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Elektronová struktura slitin india a cínu
Všianská, Monika ; Legut, Dominik ; Šob, Mojmír
The In-Sn system is interesting due to the existence of the simple hexagonal (sh) structure for compositions from 75 to 87 at% Sn at 25 ºC and from 73 to 85 at% Sn at -150 ºC. These alloys are usually referred to as gamma-Sn. Here we study the electronic structure and total energy of gamma-Sn with the help of virtual crystal approximation and demonstrate that sh structure has the lowest energy in the interval of existence of gamma-tin.
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Electronic structure In-Sn alloys
Všianská, Monika ; Legut, Dominik ; Šob, Mojmír
The InSn system is interesting by the existence of a simple hexagonal phase for compositions from 72 to 87 at% Sn at 25 °C and from 73 to 85 at% Sn at -150 °C. These alloys are usually referred to as gamma–Sn. The InSn alloys are disordered in the whole concentration interval. In this contribution, energetics and electronic structure of InSn system is studied from first principles. A simplified version of virtual crystal approximation is employed to describe disorder. It turns out that the present approach is capable of describing phase composition of InSn system in the whole concentration interval. In particular, we are able to reproduce the existence of simple hexagonal phase around 80 at% Sn.
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Energetika strukturních změn MoSi2
Káňa, Tomáš ; Legut, Dominik ; Šob, Mojmír
We employed ab initio calculations to investigate total energy profiles along the transformation paths connecting the C11b, C40 and C54 structures in MoSi2. The transformations were realized by change of the stacking sequence of the atomic planes. We found that the total energy profiles of the proposed paths have high energy barriers between end-point structures: 1.4 eV/f.u (f.u is the formula unit) for the C40-C54 path, 1.8 eV/f.u for the C11b-C40 path and finally 2.5 eV/f.u. for the C11b-C54 path.
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Studium struktury a magnetismu FeCo při vysokých deformacích z prvních principů
Čák, Miroslav ; Legut, Dominik ; Šob, Mojmír
Total energies and magnetic moments of FeCo along the tetragonal deformation path are calculated using first-principles electronic structure methods. Total energies are displayed in a contour plot as a function of tetragonal distortion and volume; borderline between the ferromagnetic and nonmagnetic states is shown. The calculated energies may be used to predict the lattice parameters of FeCo thin films on various (001) substrates; here we study the FeCo film on the MgO(001) substrate. The calculated results are compared with available experimental data. The loss of magnetism of FeCo at low atomic volumes and large shape deformations is observed.
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