The Co layer, E A is set at θ = 0°, 30°, 60°, and 90° in the simulations, respectively. Compared with the single-layer dots, the stray fields from the uncompensated magnetic poles in the Co layer influence the magnetization reversal of the Fe layer drastically. A strong E A direction dependence of the Fe layer hysteresis loops for the circle trilayer dot is illustrated in Figure 3. NOD-like receptor inhibitor As is shown, H c, M r/M s, H n, and H a are all affected. When θ = 0°, 30°, and 60°, a shift of the loop center along the field axis is obvious, which reflects the interlayer interaction directly [18–20]. The bias field H B of the Fe layer is defined from the two H n here, i.e.,

H B = (H n1 + H n2)/2, to evaluate the interaction strength, where H n1 and H n2 are click here the nucleation field of the descending and ascending branches of the loop. The bias field depending on θ is displayed in Figure 4 for different asymmetric dots. It is clearly seen that with θ increasing, H B decreases monotonically, which can be interpreted intuitively from the viewpoint of magnetic poles on the Co layer edge. However, a simple fitting with the relationship of

H B(θ) = H B(0)cosθ failed quantitatively, as also shown in the Figure. A detailed inspection in the magnetization reversal elucidates that a new S-state is formed before it evolves to a vortex in the

circle dot. This S-state is the straight result in the Fe layer to Selleckchem MLN2238 respond the Co magnetic poles. A magnetization reversal process through the S-state of a circle dot with θ at 30° is depicted in Figure 5, in which the S-state is indicated in Figure 5c. For the semicircle dots, the shape anisotropy is sufficiently strong to dominate their Etofibrate magnetization process in spite of the Co poles, leading to undetected bias effect. Figure 3 Fe layer minor loops of circle trilayer dots on easy axis direction of Co layer. The Co layer easy axis deviates from the applied field direction by the angle of 0°, 30°, 60°, 90°. The loop of a single Fe layer dot is also presented. Figure 4 The Fe layer bias field as a function of the easy axis direction of Co layer. The Co layer easy axis deviates from the applied field direction by the angle of 0°, 30°, 60°, 90°. The asymmetric dots are characterized by α = 0, 0.25, 0.5, 0.75, 1. The dash line denotes a cosine function fitting for the circle dots. Figure 5 Snapshots of magnetization reversal process through S-state of a circle dot with θ at 30°. The applied field is (a) 2,500, (b) 560, (c) 180, (d) 160, (e) - 2,320, and (f) - 2,500 Oe. The dot shows saturation, S-, vortex, and reverse saturation states in sequence. The interlayer dipolar interaction influences the stabilizing range of the Fe vortex as well.