Critical properties of strongly anisotropic ferromagnetic multilayers with dipolar interactions

Strong-anisotropy magnetic multilayers composed of two identical ferromagnetic layers separated by a nonmagnetic spacer are modeled by the Ising model including intralayer dipolar interactions and interlayer exchange coupling (IEC), where frustration emerges from the competition between interactions acting at different length scales. The effects of the IEC on the phase behavior are systematically analyzed by Monte Carlo simulations using the Wang-Landau (WL) and short-time dynamics (STD) methods. For a fixed identical ratio between exchange and dipolar constants, the temperature-IEC phase diagram at zero external magnetic field is determined. It is demonstrated that the layers reproduce the same low- and high-temperature phases as the bidimensional Ising dipolar model (IDM), namely, stripe domains and a tetragonal liquid phase, respectively. The continuous character of the transition line between these phases is independently confirmed by both WL and STD approaches. Remarkably, a scaling law for the reduced critical temperature is uncovered, characterized by a shift exponent close to the critical susceptibility exponent (γ) of the bidimensional IDM. This finding generalizes the scaling predictions previously reported for the order-disorder transition in short-range Ising bilayers to systems with long-range dipolar interactions. Furthermore, STD results reveal that the critical temperature increases monotonically with the IEC strength, reaching values up to twice the critical temperature of the IDM. This behavior demonstrates a strong IEC-induced enhancement of the thermal stability of the stripe phase, thereby extending the short-range bilayer scenario to the dipolar case. Finally, the estimated critical exponents appear to belong to the universality class of the corresponding bidimensional IDM.