The control of the direction of domain wall propagation in nanowires is important for many fundamental investigations into magnetic switching behaviour and potential applications [1, 2]. In a simple wire, this can be achieved by placing a large pad at one end of the wire to nucleate domain walls easily [2]. Where a domain wall is already present, directional control may be achieved either by using rotating magnetic fields with two-dimensional wire circuits [1] or by using a spin-polarized current [3]. Further control could be achieved by using an element that traps domain walls moving in one direction but not in the other direction. Such an element would be the magnetic equivalent of an electrical diode. Recent experimental investigations [4, 5] have demonstrated structures that perform a diode-like operation (below a critical field) on domain walls. Trapezoidal structures were used with the intention of creating an asymmetric energy barrier for a domain wall to cross. Here, we simulate the operation of Ni{sub}80Fe{sub}20 domain wall diodes by solving the Landau-Lif-shitz-Gilbert (LLG) equation. We show how the direction of motion affects the pinning of the wall and that the width of the output wire affects the diode operation. Here, domain walls are moved through the diode structure using a magnetic field, but recent experimental studies have shown that a diode-like operation is also seen using a bipolar spin-polarized current [6].
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