Domain Wall Trapping by Localized Field on Submicron Supermalloy Wires

In conventional electronic circuits, which commonly are used for information processing, digital information is represented by the existence of electron charges. In magnetic devices, which traditionally are used in data storage, information is represented by the orientation of the magnetization in small ferromagnetic elements. On the other hand, proposals also exist to solely utilize magnetic phenomena to implement logic functionality, such as magnetic quantum-dot cellular automata (MQCA) and magnetic domain-wall logic, which have promise as non-volatile and low-power devices. Furthermore, the concept of current-induced domain-wall motion has also raised significant attention since it provides a new interface mechanism between electronics and magnetism by manipulating the magnetization directly by electrons. In many of these potential applications, the controlled trapping a domain wall on a submicron ferromagnetic wire is required. In this thesis, we propose a new method of domain-wall trapping on submicron magnetic wires. In our proposal, trapping is accomplished by placing a submicron magnetic bar in the vicinity of the magnetic wire. The stray field from the bar can either aid or hinder the motion of the domain wall, and thus lead to the capture of a domain wall on the wire. Samples are fabricated on silicon wafers by means of electron-beam lithography. Supermalloy is used for both the wire and the magnetic bar. The trapping of a domain wall is confirmed by both magnetic force microscopy and magnetoresistance measurement. The trapping process is understood by means of micromagnetic simulations as well. The depinning of a domain walls is also studied in experiments. We demonstrated that the motion of a domain wall can be controlled by current pulses with assisting fields. We find that a critical current density on the order of 108 A/cm2 is required to initiate the motion. The width of the magnetic wire influences the trapping-field range of the domain walls. Simulation and experimental results indicate that for the same strength of the localized field, domain walls trapped on narrower wire require larger releasing field for depinning. Trapping domain walls by this method requires no lithographic constrictions on the magnetic wire, which provides a new prospect for the study of current-induced domain-wall motion and other magnetic devices.