Theory of the Magnetocaloric Effect

The increasing demand for energy-efficient and eco-friendly technologies is driving the search for sustainable alternatives to conventional gas-compression cooling. One of the most promising solutions is magnetic refrigeration, which uses special materials - magnetocaloric materials - that heat up or cool down when exposed to a changing magnetic field. This effect, called the magnetocaloric effect (MCE), is strongest near a materials phase transition temperature, where its magnetic state changes. Magnetocaloric materials offer great potential not only for household or industrial refrigeration at room temperature but also for low and ultra-low temperature applications, such as hydrogen liquefaction or space technologies. While the first working prototypes of magnetic refrigerators already exist, several challenges remain before the technology becomes practical and widely adopted. One major issue is the need for more efficient materials - those that offer a stronger cooling effect, work with lower magnetic fields, and can operate across different temperature ranges. Traditionally, discovering such materials has relied heavily on trial-and-error and chemical intuition. But with the growing complexity of material compositions, this method is becoming inefficient. This project aims to develop a universal theoretical model that can predict and explain the magnetocaloric behavior of materials, helping guide the search for new candidates. Fundamental thermodynamic relations that relate entropy, temperature change, and heat capacity to temperature derivatives of Gibbs free energy will form the basis for quantitative theory of MCE. This model will account the contributions of elastic, magnetic, and electronic subsystems, as well as the influence of external stimuli like pressure and stress. The goal is to develop a clear, physics-based model that explains how various factors influence a materials performance and lead to inefficiencies such as energy loss due to hysteresis. The project also aims to deepen the understanding of the fundamental physics behind phase transitions, including the identification of critical points where one type of transition shifts into another. Theoretical results will be compared with experimental data and validated in collaboration with research labs working on magnetocaloric materials. Ultimately, this work aims to speed up the development of new, efficient cooling materials and support the transition to greener, more sustainable refrigeration technologies. This research stands out by offering a general method that works for different types of phase transitions, helping scientists not only understand existing materials better but also discover new, more effective ones.