Pinning a domain wall in (Ga,Mn)As with focused ion beam lithography

Abstract

We utilize a focused beam of Ga + ions to define magnetization pinning sites in a ferromagnetic epilayer of (Ga,Mn)As. The nonmagnetic defects locally increase the magneto-crystalline anisotropy energies, by which a domain wall is pinned at a given position. We demonstrate techniques for manipulating domain walls at these pinning sites as probed with the giant planar Hall-effect (GPHE). By varying the magnetic field angle relative to the crystal axes, an upper limit is placed on the local effective anisotropy energy.

Current Induced Domain‐wall Motion in Magnetic Nanowires

“…In such nanowires, the DWs are nearly ideal Bloch walls (Wunderlich et al, 2001;Cayssol et al, 2004), with widths as small as 5 nm. In the case of (Ga,Mn)As epilayers, in-plane cubic anisotropy has been reported (Tang, Kawakami, Awschalom and Roukes, 2003), giving rise to 90 • DWs (Holleitner et al, 2004;Honolka et al, 2005;Tang and Roukes, 2004) albeit in large structures (100 µm wide).…”

“…These include notches, humps, constrictions, or crosses, which lead to potential wells (attractive) or potential barriers (repulsive) of various widths and depths. Pinning centers can also be provided by creating local modifications of the nanowire using, for example, ion bombardment (Holleitner et al, 2004) or possibly localized oxidation, localized thermal annealing treatments or by using atomic force microscopes to physically or chemically modify the nanowire (Schumacher et al, 2001). It is also possible to use magnetic materials deposited under, on, or near the nanowire to change the magnetic properties of the nanowire in localized regions.…”

Spin-polarised currents and magnetic domain walls

“…Direct atomic force microscope (AFM) lithography has been used to create point and line defects in Pt/Co/Pt out-of-plane magnetised thin film systems [137,138]. Focussed ion beam (FIB) lithography has been shown to create reproducible pinning centres in permalloy wires [139] and GaMnAs systems [140]. (At very low temperatures domain wall motion and depinning will be controlled by quantum tunelling effects [141,142].)…”

Manipulating a domain wall in (Ga,Mn)As

“…We are able to resolve the arrival of a domain wall at a pinning line through transport spectroscopy. 5 In this work, we monitor the arrival of a domain wall at the pinning line by measuring the anisotropic magnetoresistance. Temperature dependent measurements elucidate the disappearance of these effects above the ͑Ga,Mn͒As Curie temperature.…”