Investigation of the critical behaviour of n-component magnetic model

Investigation of the critical behaviour of the n-component three-dimentional (3D) magnetic model in the vicinity of the phase transition (PT) point is performed. Mathematical description based on the collective variables (CV) method. The universal characteristics of the system such as critical exponents and the critical amplitude ratios for thermodynamic functions above and below of the phase transition point are obtained, as well as non-universal ones. Calculation of the free energy in the ϱ4 model at the microscopic level is performed. Explicit analytical expression for the heat capacity is obtained. It dependence on the microscopic parameters of the system and the component number n is analyzed. The main idea of present calculations is based on the systematic consideration of contributions of the short- and long-wavelength spin density fluctuations to the thermodynamic functions of the system. As the interaction potential we use an exponentially decreasing function of the distance between the particles.