Physics Faculty Research and Publications

Application of Local Transverse Field for Domain Wall Control in Ferromagnetic Nanowire Arrays

Andrew Kunz et al. — Mon, 14 Jan 2013 10:35:14 PST

In ferromagnetic nanowire arrays, where each wire contains multiple domain walls, it will be necessary to select an individual domain wall (DW) to move. In the field driven DW case, the field is typically applied globally affecting all of the domain walls in the system. We present micromagnetic simulation results demonstrating selectivity and control of an individual DW in such an array of nanowires using a combination of global and locally generated magnetic fields. Arranging the orientation of the local field allows for selectivity of a specific DW and its controllable movement to a new location.

Injecting, Controlling, and Storing Magnetic Domain Walls in Ferromagnetic Nanowires

Andrew Kunz et al. — Wed, 07 Nov 2012 12:28:31 PST

Domain walls in ferromagnetic nanowires are important for proposed devices in recording, logic, and sensing. The realization of such devices depends in part on the ability to quickly and accurately control the domain wall from creation until placement. Using micromagnetic computer simulation we demonstrate how a combination of externally applied magnetic fields is used to quickly inject, move, and accurately place multiple domain walls within a single wire for potential recording and logical operations. The use of a magnetic field component applied perpendicular to the principle domain wall driving field is found to be critical for increased speed and reliability. The effects of the transverse field on the injection and trapping of the domain wall will be shown to be of particular importance.

Improved Magnetic Domain-wall Control with Transverse Fields

Andrew Kunz — Tue, 18 Jan 2011 09:41:35 PST

Simulations of Field Driven Domain Wall Interactions in Ferromagnetic Nanowires

Andrew Kunz et al. — Wed, 17 Nov 2010 07:57:24 PST

The interaction of domain walls in a single ferromagnetic nanowire has been observed with micromagnetic simulation. Domain walls separating domains of opposite magnetization move towards each other when an external field is applied along the long axis of the wire resulting in a collision. The final magnetic state of the wire after the collision will contain either zero (domain wall annihilation) or two (domain wall conservation) domain walls. Here we explore the behavior that determines the final state, showing that it depends on the initial domain wall configuration, the speed the domain walls are moving with before the collision, and the dimensions of the nanowire. A model is also presented which helps to determine the repulsive force the conserved domain walls exert on each other.

Dynamic Notch Pinning Fields for Domain Walls in Ferromagnetic Nanowires

Andrew Kunz et al. — Wed, 17 Nov 2010 07:47:30 PST

Artificial defects such as notches and antinotches are often attached to magnetic nanowires to serve as trapping (pinning) sites for domain walls. The magnetic field necessary to release (depin) the trapped domain wall from the notch depends on the type, geometric shape, and dimensions of the defect but is typically quite large. Conversely we show here that for some notches and antinotches there exists a much smaller driving field for which a moving domain wall will travel past the defect without becoming trapped. This dynamic pinning field also depends on the type, geometric shape and defect dimensions. Micromagnetic simulation is used to investigate both the static and dynamic pinning fields and their relation to the topologic structure of the domain wall.

Magnetic Response Versus Lift Height of Thin Ferromagnetic Films

Tanner Schulz et al. — Wed, 17 Nov 2010 07:24:54 PST

The interaction between a magnetic force microscope (MFM) tip and ferromagnetic films of Ni, Co₉₀Fe₁₀ and Py with in-plane magnetization has been investigated. The measured interaction, due to the magnetizing of the films by the MFM tip field, was determined by the phase shift of the cantilever response. The tip-film separation or lift height dependent phase shift was found to be independent of the saturation magnetization of the ferromagnetic film. The result is identical for all three films and micromagnetic simulations give similar results. The reason is at a given tip-sample separation the tip induced magnetization of the film creates a demagnetization field which is equal in magnitude to the tip field at that separation.