Monte Carlo study of the surface effect on the compensation and critical behaviour in a molecular-based magnetic film AFeIIFeIII(C2O4)3

Monte Carlo simulation is used to study the magnetic properties and critical behaviour of a molecular-based magnetic film AFe(II)Fe(III)(C2O4)(3)(A = N(n-CnH2n+1)(4), n = 3-5). The effects of surface exchange coupling, surface single-ion anisotropy and layer thickness on the compensation temperature and critical temperature of a ferrimagnetic mixed spin-2 and spin-5/2 Ising model on a honeycomb lattice are discussed in detail. The results show that the surface intralayer exchange coupling R-1 = J(1S)/vertical bar J(1)vertical bar and surface interlayer exchange coupling R-2 = J(2S)/vertical bar J(1)vertical bar play important roles in the compensation and critical behaviour of the system. In particular, we have found two special points R-1c at which the compensation and critical temperatures are independent of the layer thickness L and the surface single-ion anisotropy D-1S/vertical bar J(1)vertical bar. A number of characteristic phenomena, such as the possibility of two and three compensation points, are found. The effects of the layer thickness L on the susceptibility, internal energy and specific heat with temperature are numerically investigated.