The magnetic and hysteretic characteristics of bilayer graphene nanoribbons: a comparative study by the Monte Carlo method

Driven by the recent progress in graphene nanoribbons, particularly with regard to their implementation in spintronic applications, we employ here the Monte Carlo simulation to perform a comparative analysis of the magnetism of two ferrimagnetic bilayer nanoribbons (BNRs) consisting of a mixture of spin-3/2 and spin-1/2, featuring rectangular and hexagonal shapes. We thoroughly examine how exchange couplings and the crystal field affect the phase diagrams and the magnetic properties, including magnetizations, magnetic susceptibility, internal energy, and specific heat. The exact calculations derived from the Hamiltonian at the ground state (T=0) unveil the existence of distinct lines delimiting various ground states. The phase diagrams indicate that the rectangular (BNR) may exhibit double compensation temperatures and triple loops hysteresis behaviors for well-determined values of exchange couplings (Jσ, JS, and JσS) as well as the crystal field DS. In contrast, one compensation point and only a single hysteresis loop characterize the hexagonal (BNR). However, the insertion of DS results in the emergence of triple loops.