Modeling and study of quasi-two-dimensional magnetic materials

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..

Modelování a studium kvázi-dvourozměrných magnetických materiálů

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...Dzyaloshinskii-Moriya interakce (DMI) je druh výměnné interakce přítomný v necen- trosymetrických strukturách. Způsobuje natáčení (canting) spinů a je to důležitý me- chanismus stabilizace nekolineárních magnetických struktur, například skyrmionů, které mají aplikační potenciál ve spintronice. Dále hraje DMI důležitou roli v multiferoikách a podporuje magnetoelektrický jev. Oba tyto jevy jsou často pozorovány ve vrstevnatých materiálech. Tato práce zkoumá, skrz numerické simulace, efekt out-of-plane DMI (ve směru kolmo na rovinu) na magnetické uspořádání na dvourozměrné triangulární mřížce. Využívá kla- sický Heisenbergův model spolu se simulačními metodami Markov Chain Monte Carlo a spinové dynamiky. Kromě DMI obsahuje Hamiltonián modelu také feromagnetickou výměnnou interakci mezi nejbližšími sousedy a interakci s externím magnetickým polem. V první části jsou vypočítány vlastnosti systému za nulové teploty pro různé síly DMI a externího magnetického pole a je zkonstruován fázový diagram. Jsou pozorovány tři různé fáze: feromagnetická, antiferomagnetická cykloidální a kónická, která je kombinací předchozích dvou. Druhá část se zaměruje na vlastnosti systému za konečné teploty, počínaje měrnou tepelnou kapacitou, magnetizací a magnetickou susceptibilitou. DMI neovlivňuje kritic- kou teplotu uspořádání, ale...Katedra fyziky kondenzovaných látekDepartment of Condensed Matter PhysicsFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

A fully unprivileged CernVM-FS

The CernVM File System provides the software and container distribution backbone for most High Energy and Nuclear Physics experiments. It is implemented as a file system in user-space (Fuse) module, which permits its execution without any elevated privileges. Yet, mounting the file system in the first place is handled by a privileged suid helper program that is installed by the Fuse package on most systems. The privileged nature of the mount system call is a serious hindrance to running CernVM-FS on opportunistic resource and supercomputers. Fortunately, recent developments in the Linux kernel and in the Fuse user-space libraries enabled fully unprivileged mounting for Fuse file systems (as of RHEL 8), or at least outsourcing the privileged mount system call to a custom, external process. This opens the door to several, very appealing new ways to use CernVM-FS, such as a generally usable “super pilot” consisting of the pilot code bundled with Singularity and CernVM-FS, or the on-demand instantiation of unprivileged, ephemeral containers to publish new CernVM-FS content from anywhere. In this contribution, we discuss the integration of these new Linux features with CernVM-FS and show some of its most promising, new applications