Kosterlitz-Thouless Phase Transitions and Phase Diagram of Ultrathin Ferromagnetic Films.

M. A. BAB; G P SARACCO

Congreso; 2020 Express Conference on the Physics of Materials and its application in Energy and Environment; 2020

Cinvestav

Ultrathinmagnetic films with strong out-of-plane anisotropy have been modeled by meansof ferromagnetic Ising model with dipolar interactions. The phase diagram atzero external field presents a rich phenomenology that includes low-temperaturephases characterized by stripes (h) and a high-temperature phase with domainsof stripes with mutually perpendicular orientations, tetragonal liquid (TL).The latter can be reached by two possible ways: direct transition h-TL or by anintermediate phase with orientational order but short-range positional disorder(nematic NM). The regions of the phase diagram where these transitions occur,and its character have been the object of a long-standing controversy. IntensiveMonte Carlo simulations were performed for selected values of the ratio betweenthe ferromagnetic exchange and dipolar constants (d). The results indicate thatthe NM phase is present for d ≥2, and both h-NM and NM-TL phase transitions areKosterlitz-Thouless type