Field-Driven Domain Wall Motion in Notch-Patterned Permalloy Nanowire Devices

• Main Authors: Pei-Chu Tsai, 蔡珮渠
• Other Authors: Jong-Ching Wu
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/77097749539620611958

碩士 === 國立彰化師範大學 === 物理學系 === 103 === Based on the current advancement of information fast electronic processing speed and ultra-high storage capacity are needed. Recently, the development of Spintronics has given promising applications in the fields of logic processing and data storage/memory. Therefore, many efforts have been devoted to investigate the relevant issues such as magnetic domain wall (DW) motion in magnetic nanowires (NWs). In this thesis, the formation and propagation of magnetic domain walls in ferromagnetic nanowires are presented. Nanometer Permalloy wires with one end connected with a micron circular pad and the other end sharpened are fabricated along with alternative upward/downward triangular notches. The micron circular pad is acting as domain wall launching pad, sharpened end is made to prevent domain wall nucleation, and notches are designed to be the pinning sites. In such a design, the pinning and depinning of the magnetic domain walls may be observed by an applying external magnetic field along the nanowires. The planar Permalloy nanowires with various widths of 350, 500 and 550 nm are fabricated on Si/SiO2 substrate by using standard electron beam lithography through a lift-off process. The Permalloy was thermally evaporated with thickness being controlled to be around 25 to 30 nm. The lengths of the nanowires are tens of micrometers, and the depths of triangular notches are nearly half of the nanowire’s widths. The dynamics of the domain walls has been investigated by an in-situ magnetic force microscopy (MFM). The MFM micrographs are taken in the presence of continuous and pulsed in-plane magnetic field applied along the long axes of the wires. In addition, micromagnetic simulations using both OOMMF and MuMax3 are carried out to analyze the propagation behavior of the domain walls through the Permalloy nanowires. The experimental results show the domain wall nucleates from the circular pad and propagates along the nanowire. Under the continuous magnetic field, the domain walls are only pinned at the first or at the second notch followed by DW propagation to the other end of the NWs and thus the reversal processes are finished. In case of pulsed magnetic field, repeated measurements occasionally show the domain walls are pinned at different locations in the different runs. Furthermore, the domain walls are pinned at many notches in the nanowires with smaller widths. Therefore, by using the pulsed field with different duration, number of times, and magnitude of field can control the location of DW in the nanowires.