Optimization of magnetocaloric effect in molecular magnets within the Hubbard model

In this work, we present a systematic study of the magnetocaloric effect (MCE) in molecular magnets modeled by the Hubbard Hamiltonian. Using the exact diagonalization method, we examine the influence of the Hubbard interaction (U), cluster size (L), geometry, and electron filling (N) on the cooling and heating properties of these systems, with the main goal of optimizing the magnetocaloric refrigeration. Our analysis reveals several interesting results: (i) Intermediate values of U([Formula: see text]) provide the best cooling effect, surpassing both the behavior of purely localized electrons at large U as well as delocalized ones at small U; (ii) Increasing the cluster size improves cooling ([Formula: see text]), but reduces its efficiency relative cooling power (RCP), indicating that smaller clusters may offer more efficient refrigeration; (iii) Regular polygons effectively suppress undesired heating effects and produce a higher RCP than linear chains; and (iv) Maintaining the half-filled condition [Formula: see text] is essential for achieving optimal magnetocaloric performance. These results could contribute to the design of materials with enhanced magnetocaloric properties, offering promising applications in energy-efficient cooling technologies.