Frustration in coupled magnetic thin films due to competion between exchange and dipolar interactions

BAB, MARISA ALEJANDRA; G P SARACCO; J.J. MELO QUINTEROS; P. S. PAGLIARO

Trieste

Congreso; Statistical Physics of Complex Systems; 2021

ICTP

The observation of alternated strip magnetic domains in monolayered films has beenreported when perpendicular anisotropy is present. The case of astrong perpendicular anisotropy (SPA) has been modelled by the 2d-ferromagneticIsing model adding dipolar interactions. This term induces frustration due to the competition with the exchange interaction, so structures with net zero magnetization appear. The phase diagram exhibits many phases and transitions of different kind. At low temperatures, antiferromagnetic and alternated spin stripesof width h emerge, where h increases with the exchange and dipolar constant ratio δ=J/g. At higher temperatures, a tetragonal-liquid phase(TL) takes place, where the spin stripes intersect perpendicularly. Furthermore,it was found an intermediate nematic phase for δ>= 2.  The phase transitions can be first, second order or the Kosterlitz-Thouless type. On the other hand, when two ferromagnetic SPA films are separated by a nonmagnetic layer, the interlayer coupling is RKKY like, i.e., presents a damped oscillation from ferro to antiferromagnetic with the thickness of the nonmagnetic layer. This fact leads to a complex phase behavior, whose study by means of Monte Carlo simulations is the goal of this work. For doing this, the exchange and dipolar constants are fixed to obtain stripes with different width on each film, and the interlayer coupling is varied to have aferro or antiferromagnetic interaction. The equilibrium configurations atdifferent temperatures and the phase transitions are characterized and compared in relation to the respective monolayer phase behavior for the same values of δ.