Investigation of the Magnetocaloric Effect in Correlated Metallic Systems with Van Hove Singularities in the Electron Spectrum

In this work, the magnetic contribution to the isothermal entropy change Delta S upon switching on a magnetic field has been investigated in correlated metallic ferromagnets within the Hubbard nondegenerate model. The analytical expression for Delta S obtained in the mean-field approximation depends substantially on the electronic structure (density of electron states), which presents new ways to increase the absolute value of Delta S relative to the known result obtained within the Heisenberg model. The temperature dependence of Delta S has been calculated at different values of the Coulomb interaction U and the number of electrons n for the Bethe infinite-dimensional lattice and square lattice with allowance for transfer integrals in the first (t) and the second (t') coordination shells. It has been found that the presence of Van Hove singularities in the electronic spectrum near the Fermi level makes it possible to considerably increase vertical bar Delta S vertical bar at a fixed magnetic field. The possibility of first-order magnetic phase transitions depending on the model parameters has been analyzed.