Canted stripe phase near the spin reorientation transition in ultrathin magnetic films

Abstract

Results from computer simulation and numerical studies for the ferromagnetic Heisenberg model on a square lattice are presented. The model includes the exchange and dipolar interactions as well as the magnetic anisotropy. The analysis focuses on the nature of the stripe phase which determines the phase behavior of this system close to the reorientation transition for a particular value of the exchange constant corresponding to $\mathcal{J}=8.9$ in reduced units. The results show that as the perpendicular anisotropy parameter $\ensuremath{\kappa}$ is increased from zero, the system undergoes a reorientation transition from the planar ferromagnetic phase to the stripe phase. Both the simulations and ground state calculations show that the stripe phase consists of two distinct regions. For large values of $\ensuremath{\kappa}$, the spins are aligned, on average, perpendicular to the plane with properties qualitatively similar to those observed for the dipolar Ising model. Close to the reorientation transition, there exists a narrow range of $\ensuremath{\kappa}$ in which the perpendicular components of the spins align to form stripes, but with the spins canted toward the plane giving rise to a net transverse magnetization. We present a phase diagram based on the results from the numerical calculations and simulation studies and discuss connections with earlier theoretical and simulation studies, as well as experiments on ultrathin magnetic films. In particular, we draw attention to similarities between the results presented in this study and the so-called temperature gap (or pseudogap) region observed experimentally at the reorientation transition in ultrathin magnetic films. We also discuss the extent to which the results of these studies support the conclusion that the three types of magnetic order observed in these studies represent distinct thermodynamic phases.