Depinning field of domain wall in wide wire with asymmetric notch

Deng-Shiang Shiu^1*, 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, email:h910290@hotmail.com

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 (H_d) 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 H_d. We measured H_d 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. H_d is dependent on wire width and θ of notch. Figure 2 shows the H_d decrease as wire width increase. This result is similar to our simulation. Fitting lines trend in figure 2 are different to simulation. In H_d 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