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(a) SEM image of a nanowire with asymmetric notch, where A and B designate the positions where MOKE measurement are performed. The insets show the structure enlargement of the asymmetric notch with (b) SEM image and (c) schematic illustration.
(a) Magnetic hysteresis loop measured at spot “A” of the nanowire, it shows that the propagation field of the DW is about 56 Oe. (b) Hysteresis loop measured at spot “B” shows the depinning fields from the notch. Two-step jumps are found at ∼190 and ∼260 Oe, respectively. All the loops are obtained by averaging 20 ∼ 30 times measurements to achieve reasonable signal-to-noise ratio.
Statistical study of successive depinning events by focused MOKE measurements. Two typical individual magnetization switching processes measured at spot “B” are shown in (a) and (b), where the depinning fields are 260 Oe and 190 Oe, respectively. (c) Randomly distributed depinning fields within 40 times measurements. (d) Gaussian distribution of depinning fields for 100 times measurements.
Zoom-in plots show the depinning process from an asymmetric notch for two vortex DWs with opposite chiralities: (a)–(e) for a clockwise vortex DW and (a')–(e') for the counter-clockwise vortex DW. (a) and (a') are the initial remanent states of the two vortex DWs (enhanced online). [URL: http://dx.doi.org/10.1063/1.4745788.1]10.1063/1.4745788.1
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