Micromagnetic Study of Controllable Domain Wall Motion in Ferromagnetic Nanowire Arrays via Transverse Magnetic Fields

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TECHNICAL SUMMARYThis award supports theoretical and computational research and undergraduate education efforts on ferromagnetic materials and magnetization dynamics.Undergraduate physics majors will be supported by this award to conduct research on understanding the processes necessary to control a single domain wall in an array of ferromagnetic nanowires each of which contain multiple domain walls. Domain wall motion is being intensely investigated due to a variety of interesting physical properties and potential applications in data storage and sensing. However the bulk of the research efforts have been focused on the behavior of one domain wall in a single wire. The viability of the technologies here depends on the ability to manipulate a given domain wall in large arrays of wires. Since each domain wall in the system potentially responds to the driving mechanism, techniques need to be developed to select and control a given domain wall.The PI has identified an important characteristic of domain wall motion which has the potential for improving selectivity and control. Local magnetic fields applied along the primary domain wall magnetization direction, a transverse field, can be used to select a particular domain wall and to move it reliably. Because the transverse field gives additional pressure to a domain wall the combination of the transverse field and the overall driving mechanism, which could be an external field or a spin-torque applied by a current, can be used for selection. New theories will be developed to assist in explaining the overall behavior and predict reliable combinations. Micromagnetic simulation is an ideal tool for this research as the technique allows for picosecond time resolution with concurrent nanometer spatial resolution; each of which is necessary for accurately depicting the high speed magnetization dynamics. The tool is accessible to undergraduates and additional computer programming and theoretical efforts will be combined to analyze and understand the results. The PI and Marquette University are committed to encouraging underrepresented groups in the STEM fields to participate in research. Local outreach efforts will be continued with the help of this award and research by the PI and his students. NONTECHNICAL SUMMARYThis award supports computational and theoretical research on ferromagnetic nanowires by undergraduate physics majors. Nanowires are very tiny wires that are some 10,000 times smaller in diameter than a human hair.In a magnetic material a domain wall forms between two regions of oppositely oriented magnetism. When formed in a nanowire, devices have been demonstrated in which the high- speed motion of a domain wall is used: to carry out logic operations, for high capacity data storage, and as sensors via varying magnetoresistance. In addition to increased data storage capacity, magnetic devices are non-volatile, consume less energy, and have operational speeds significantly faster than today's technologies. These devices will necessarily consist of multiple ferromagnetic nanowires each containing multiple domain walls, but the majority of the prior effort in understanding domain wall motion has focused on single domain walls in a single wire. This award will be used to develop techniques to control an individual domain wall, in the presence of other domain walls with which there will be interactions, through an individual wire in the array. The project engages undergraduate physics majors to participate in carrying out computer simulations and theoretical modeling. The computer simulations follow an equation of motion for each tiny magnetic region in the nanowire. The equation of motion is essentially a torque equation and as such is easily accessible to undergraduate physics majors. Students benefit from the research experience which in the process adds to their education in magnetic materials and nanotechnology. Some of the simpler interpretations and results are used for current topics in introductory courses to highlight the importance of classical physics in modern research and technology and models have been developed to use in outreach efforts. The PI is committed to providing opportunities for students underrepresented in the STEM fields.