Magnetic properties of armchair graphene nanoribbons: A Monte Carlo study

The magnetic properties of armchair graphene nanoribbons have been studied using a Monte Carlo study. The ground state phase diagrams have been determined for mixed spins S={±2; ±1; 0} and σ={±5/2; ±3/2; ±1/2}. The topologies of the phase diagrams depend on the values of the parameters in the Hamiltonian such as exchange interactions, crystal field and external magnetic field. The some diagrams show some coexistence between regions. The Néel temperature t_N is obtained for different values of layer (n). The effect of reduced exchange interactions between the mixed spins σ and S and reduced crystal field on total magnetization has been given. Magnetic hysteresis cycles are given for different values of n, reduced exchange interactions and reduced temperatures. The double hysteresis loop and superparamagnetism were observed.