Depinning field of domain wall in wide wire with asymmetric notch
Deng-Shiang Shiu1*, Yun Hong1, Chin-Han Su1, Kao-Fan Lai1, Jong-Ching Wu1, Lin Lin1, Yee-Mou Kao1
1Physics, National Changhua University of Education, Changhua, Taiwan
* Presenter:Deng-Shiang Shiu,
We employed 20-nm-thick NiFe wire with asymmetric notch and different width wires for investigating vortex domain wall (VDW) with clockwise (CW) and counterclockwise (CCW) chirality depinning field (Hd) in micron size wire. The devices were been fabricated by e-beam lithography and magnetron-sputtering. Wire width was designed for five different widths ranging from 1 μm to 3 μm with 0.5 μm increase. The asymmetric notch is designed with different asymmetric angle (θ) with depth ratio of ~0.5 (notch depth divided by wire width) at left side of notch for inspecting Hd. We measured Hd about 20 to 30 times by MOKE microscope, and get magnetic images. We simulated 0.2, 0.4, 0.6 and 0.8-μm-wide wires with notch by MuMax3 to assist us better understand DW motion. Magnetic images of our simulation showed depinning process are similar to experiment images. Hd is dependent on wire width and θ of notch. Figure 2 shows the Hd decrease as wire width increase. This result is similar to our simulation. Fitting lines trend in figure 2 are different to simulation. In Hd v.s. θ curve of our simulation results, fitting line slope of tail to tail (TT) type VDW with CCW and CW chirality in 0.2-μm-wide wires are about 0.56 and 0.97 respectively; fitting line slope of TT type VDW with CCW and CW chirality in 0.6-μm-wide wires are about 0.23 and 0.45 respectively. In micron-size wire, VDW with small Hd has low energy density. Length of notch left side has more influence than submicron-size wire for VDW with low energy density.

Keywords: Magnetic vortex domain wall, MOKE microscope, Field driven domain wall, Thin film