Thermodynamic properties and magnetization processes of magnetically dipole-coupled bilayer film with in-plane and perpendicular anisotropies

Abstract A bilayer ferromagnetic film model with in-plane anisotropy and out-of-plane anisotropy is established in the x-y plane and described by the Heisenberg model, in which the intralayer exchange interaction and interlayer magnetic dipole-dipole interaction are taken into account. The thermodynamic properties and magnetization behaviors of the system are investigated by means of the microscopic mean-field Monte Carlo (MMFMC) simulation method. Due to the relatively weak strength of interlayer dipole interactions, the thermodynamic properties of the bilayer system exhibit both single-layer characteristics and overall collective features. Two inflection points emerge in the temperature dependence of magnetic internal energy, accompanied by two distinct sharp peaks in the magnetic specific heat at the corresponding temperatures. The longitudinal and transverse magnetic susceptibilities show prominent peaks near the respective transition temperatures of each individual layer. Meanwhile, the overall z-direction magnetization is enhanced, the two susceptibility peaks tend to merge, and the in-plane magnetization is weakened.Magnetic hysteresis emerges in the system under applied magnetic fields both parallel and perpendicular to the film plane. The coercivity of the out-of-plane hysteresis loop increases with the enhancement of dipole coupling strength. A similar variation trend is observed for the in-plane coercivity under strong in-plane anisotropy. In contrast, when the in-plane anisotropy is weak, the in-plane coercivity decreases as the interlayer dipole interaction strengthens.