The Spin Reorientation Transition and Phase Diagram of Ultrathin Ferromagnetic Films

Carubelli, Marianela
Billoni, Orlando V.
Pighin, Santiago
Cannas, Sergio A.
Stariolo, Daniel A.
Tamarit, Francisco A.
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We show results from Monte Carlo simulations of a two dimensional Heisenberg model for ultrathin films with perpendicular anisotropy. A complete phase diagram is obtained as a function of anisotropy and temperature, spanning a wide range of behavior. We discuss our results in relation with experimental findings in different ultrathin films. We observe and characterize a line of Spin Reorientation Transitions . This transition from out of plane stripe order to in plane ferromagnetic order presents a paramagnetic gap in between in a finite region in parameter space, as reported in experiments. For large anisotropies direct transitions from a low temperature stripe phase to a paramagnetic or tetragonal phase with dominant perpendicular magnetization is observed, also in agreement with experiments. We also show the phase diagram for a system without exchange, i.e. with pure dipolar and anisotropy interactions. It shows a similar behavior to the ferromagnetic case with antiferromagnetic instead of stripe phases at low temperatures. A Spin Reorientation Transition is also found in this case.
Comment: 9 pages, 13 figures
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Statistical Mechanics