A new route towards synchronous domain wall motion

: studying precession torque effects in nanostrips with perpendicular magnetic anisotropy

Abstract

Magnetic domain wall motion is an intensively studied subject because of its possible applications for data storage. High density, non-volatile computer memories could be fabricated if novel concepts based on domain wall motion are realized. In this thesis domain wall motion, using an unconventional driving mechanism based on the precession torque, is studied.Precession torque driven domain wall motion in magnetic nanostrips with perpendicular magnetic anisotropy, PMA, is investigated both theoretically and experimentally. The theoretical investigation is done using a collective coordinates model and object oriented micromagnetic framework simulations. Both methods show that when an in-plane magnetic field pulse is applied to a domain wall in a PMA system, the domain wall is indeed moved by the precession torque. When realistic values of the material parameters are used, high domain wall velocities, in the order of 100 m/s, are predicted. The influence of the strength of the applied pulse, Gilbert damping parameter and the chirality of the domain wall are investigated and the observed behaviour is discussed.Experimentally, we study the depinning of domain walls as a function of the applied in-plane field pulse and the results are compared to quantitative predictions from the model. The observed behaviour does not correspond to the predictions. Further analysis indicates that in order to observe effects from the precession torque, pulses with a rise time in the order of a nanosecond are required, a requirement not fulfilled in our setup.During the experiments, we observed a chiral dependence of the domain wall depinning on static in-plane fields along the nanostrip. This unexpected behaviour can be explained by the Dzyaloshinskii-Moriya interaction, DMI. This allows for a novel way to study the DMI, using well-defined structures and relatively simple measurements.

Date of Award	31 Aug 2014
Original language	English
Supervisor	Henk J.M. Swagten (Supervisor 1) & J.S. Kim (External coach)