Monte Carlo studies of the first order phase transitions on a mixed spin-2 and spin-5/2 system

The first order phase transition of mixed spin-2 and spin-5/2 Ising system in honeycomb lattice with two single ion anisotropies is studied by Monte Carlo (MC) simulation. We have investigated in detail the regime of anisotropies where first order phase transition can occur as the temperature increases. The results show that only when the single ion anisotropies are located around the critical line separating the order and disorder ground states will the first order phase transition arise, which contests the previous studies obtained by mean-field theory (MFT). In addition, interesting magnetic changes around the two critical points of anisotropies are found and all the results are related to the magnetic behavior of a molecular based magnet.