Insights into Magnetic Properties of an Ising Nanoisland with Four-Spin and Next-Nearest Neighbor Interactions

We propose a multi-spin Ising model to report a computational study of a mixed spin-1 and spin-1/2 ferrimagnetic nanoisland. Employing the finite cluster approximation (FCA), we thoroughly examine how the four-spin interaction, next-nearest neighbor interaction, and crystal field affect the phase diagrams and the magnetic properties including magnetizations, internal energy, and specific heat. The exact calculations derived from the Hamiltonian at the ground state (T = 0) reveal the existence of a critical equation, J′ + J₄ = − 4J_s delimiting two distinct ground states (I) and (II). Phase diagrams analysis shows that the transition temperature T_c trends toward a tricritical point as the four-spin interaction J₄ varies, without evidence of compensation phenomena; while the next-nearest neighbor interaction J' leads to the manifestation of compensation points only if J′ surpasses a J_s-dependent threshold value. Interestingly, when the crystal field D_S is inserted, one, two, or three compensation points may emerge according to the strength of J′.