The shape asymmetry BMS-907351 in vivo is induced by cutting a section of the circle dot characterized by a parameter α = a/r, as illustrated in Figure 1, where a is the cutting distance from the circle center and r the circle radius. The field is applied along the cutting direction and makes an angle θ to the Co layer E A. Figure 1 Micromagnetic model of a trilayer dot. The shape asymmetry of the dot is induced by cutting a section of the circle dot characterized by a parameter α = a/r.

The field is applied along the cutting direction and makes an angle θ to the Co layer easy axis. Results and discussion At first, we focus on a single-layer dot of Fe, i.e., the competition between the exchange and the dipolar magnetic energy affecting the vortex state. Except the α = 0 semicircle dot which has a rather square hysteresis loop, the other dots with α = 0.25, 0.5, 0.75, and 1 display more or less constricted loops which is typical of magnetization reversal via a vortex state. Figure 2

shows the geometric asymmetry dependence of the hysteresis coercivity H c, remanence ratio M r/M s, vortex nucleation field H n and annihilation field H a. The circle dot (α = 1) has a negligible coercivity, near-unity remanence ratio, the smallest H n, and the largest H a, as expected. When the selleck α value decreases, both of H c and H n increase monotonically because the shape anisotropy is gradually enhanced along the field direction which favors a coherent rotation of the magnetic moment. However, the M r/M s and H a present nonmonotonic behavior. For example, the M r/M s value decreases from 0.98 to a minimum of 0.71 and subsequently ascends to 0.93 at the semicircle dot. This behavior is also found by NM Vargas and co-workers [5, Doxorubicin 8] and is explained as a consequence of the competition between exchange, local dipolar interactions, and geometry effect. The cutting surface facilitates the emergence of a C-state due to the elimination of the magnetic poles on it, which decreases the remanence. When the asymmetry further increases, the shape anisotropy dominates the magnetization reversal, leading to the remanence increase. Besides,

the more deviation from a circle, the more difficult for the dot to accommodate a vortex, which demonstrates the descending H a. The semicircle dot, although, shows a square loop, which SB202190 purchase reverses its magnetization through vortex nucleation and fast propagation, resulting in the same value of H n and H a in the simulations, as shown in Figure 2b. As the vortex nucleation site is fixed at the center of the cutting surface, the vortex chirality is determined by the external magnetic field direction conveniently in these asymmetric dots. Figure 2 The asymmetric α dependence of the magnetization parameters of a single Fe layer dot. (a) Coercivity and remanence ratio. (b) Vortex nucleation field and annihilation field vary with α value.