Magnetic domain wall dynamics in nanoscale thin film structures

Abstract

The dynamics of individual magnetic domain walls in permalloy nanowires fabricated through focused ion beam patterning is presented in this dissertation. The motion of an individual domain wall is detected directly via magneto-optical Kerr polarimetry. In the basic measurement, the velocity of the domain wall is measured over a range of external driving magnetic fields. The velocity measurement is found to have two distinct linear regions separated by a region with a negative differential. This measurement is then expanded upon by varying the width of the nanowire and applying a DC current though the nanowire. The means by which the domain wall enters the nanowire from a continuous film is investigated. A pinning potential traps the domain wall at the interface between the nanowire and continuous film at low magnetic fields. Fields below the critical “injection” field allow the domain wall to overcome the pinning potential through a thermal activation mechanism. The critical injection field is found to depend on the width of the nanowire. A moving domain wall has been found to create a voltage across the nanowire through which it traverses. The voltage produced is proportional to the velocity of the domain wall and is on the order of hundreds of nV.