Doctoral School of Physical Sciences
The magnetic refrigeration technique based on magnetocaloric effect (MCE) represents the most promising alternative to gas compression refrigeration. The MCE can generate substantial temperature changes around room-temperature, particularly in materials undergoing simultaneous magnetic and structural transitions. In magnetocaloric materials (MCMs), the alignment of randomly oriented magnetic moments by external magnetic field at adiabatic conditions results in heating. This heat is removed by heat transfer. After turning off the magnetic field the magnetic moments randomize again cooling the material below the ambient temperature. Practical implementation of the magnetic refrigeration technique requires the development of innovative MCMs, having superior magnetic, chemical and mechanical properties and at the same time admissible cumulative cost and low environmental burden. A divers set of first-principles modeling tools will be used, being the most appropriate for a particular problem within the MC process described above. To perform calculations for multi-component solid solution phases the coherent potential approximation (CPA) will be employed, implemented within the framework of the Exact Muffin-Tin Orbitals (EMTO) method developed within the group. Other tools will be introduced as needed during the studies. The PhD student will gain extensive knowledge about all these methods, which will be applied to obtain deep insight into the recently developed multi-principal-element-alloys showing promising properties for magnetocaloric applications. Systems based on transition metals will be considered avoiding heavy elements and other critical raw materials. The primary alloys will be built around Cr-Mn-Fe-Co-Ni with variable compositions and encompassing small amounts of non-magnetic elements such as Al, V, Cu, etc. used to tailor the phase stability. The PhD candidate will adopt the above theory-based design strategy to establish extensive composition-properties maps. These maps will be used to identify single or multi-phase alloys where the magnetic state is coupled with the vibrational degree of freedom and phase stability, implying an enhanced lattice entropy contribution upon magnetic transition. Selected solutions will be tested by experimentalists within the Centre. The project will be performed in close collaboration with the group of Prof. Levente Vitos (KTH, Stockholm), including visits if needed.
The candidate is required to be knowledgeable in solid state physics, basic quantum mechanics, magnetism and should be affine to computational methods.
PhD project for Stipendium Hungaricum