Welcome to this instructional site. Following are several examples of the motion of domain walls under the
application of external magnetic field.
The images were taken by using magnetic force microscopy (MFM) in the presence of external applied fields.  The "field lapse" animation consists of about
35 MFM images in one complete cycle. The data start at remanence, and taken in succession in progressively varying field --- first ascending to about 120 Oe, descending
through zero to -120 Oe and back again to zero.
Special MFM probes were selected which had very low moments in order to reduce tip-induced image perturbation.
The caveat however, is that the small field from the tip may induce profound changes, specially when the external
field is close to some critical value which causes drastic
magnetization changes. The samples were furnished by K.J. Kirk and J.N. Chapman of the Dept. of Physics and
Astronomy, University of Glasgow, Scotland.
The films were thermally evaporated on silicon substrates and patterned
using e-beam lithography.
It takes approximately to load the animation sequences at 20KPS, and the best results are obtained with the latest version of Navigator. If some animations stall, try clearing or increasing the memory cache of Navigator (Edit/Preferences/Advanced(2x)/Cache) and reloading.
A special welcome is extended to conference attendees of the MMM'98 Conference, and to my numerical micromagnetic modeling colleagues.
|Domain wall motion of a 3 micron x 3 micron x 26 nm thick Permalloy element in one magnetization cycle. At remanence (H=0), the configuration is a 7 domain closure pattern with eight 90 degree walls and two horizontal near 180 degree walls. The right 180 degree wall is itself divided into 2 Bloch lines and 1 crosstie, thus giving the appearance that the rightmost segment is divided into 2 subsections. (SEE General comments below for a description of Bloch lines and crossties and how they are indentified in MFM.) With increasing field along the vertical axis, the right and left segments (which are parallel to the field) expand at the expense of the middle segment. Note that the left segment, perhaps due to the absence of a crosstie, expands more rapidly than the left. Technical saturation is achieved as soon as the domains have coalesced. Reduction of the field back to zero generates a complex domain structure with curved and discontinuous domain walls, but a slight negative field (immediately after remanence) induces a transition into the familiar (classic textbook) 4 domain closure pattern.|
|Domain wall motion of a 4 micron x 3 micron by 26 nm thick Permalloy element in one magnetization cycle. At remanence (H=0), the configuration is a 4 domain closure pattern with 90 degree strained walls. Note the motion of the central vortex, and the formation of complex edge structures prior to near saturation. The formation of a crosstie on the left edge near saturation is particularly interesting. The mechanical defect (circular protrusion) appears to induce a slight bending of the moving "90 degree" wall.|
|Domain wall motion of a 3 micron x 2 micron by 26 nm thick Permalloy element in one magnetization cycle. At remanence (H=0), the configuration is a 4 domain closure pattern with four 90 degree walls and one horizontal 180 degree wall. Note the creation and motion of a Bloch line at intermediate fields (+/- 30 Oe). The mechanical defect (diagonal strip across the lower right corner) appears to induce the slight motion of the vortex near saturation.|
|Domain wall motion of a 4 micron x 2 micron by 26 nm thick Permalloy element in one magnetization cycle. At remanence (H=0), the configuration is a 4 domain closure pattern with 90 degree walls, a 180 degree wall with 2 Bloch lines and a crosstie at the center. During the ascending branch of the magnetization, the right domain increases in size and accompanied by the corresponding reduction of the left. Note that prior to coalescence with the growing right domain, the crosstie at the center remains stationary, albeit, the intensity diminishes and cants towards the growing right domain. The crosstie was observed only during the initial remanent state and in the ascending branch, but not during the descending branch and negative field. The sudden contrast flip of the 180 degree wall (near coercivity) indicates the reversal of the charges on the 180 degree wall. This is enigmatic.|
More details can be found in the following articles:
R.D. Gomez, et al., "Domain configurations of submicron Permalloy elements" and "Domain wall motion of nanostructured Permalloy Islands", J. of Applied Physics 1999, in press.
The above analyses are solely due to the author and the viewer is welcome to offer other insights. Send comments or preprint requests to firstname.lastname@example.org.
Check out a similar animation for single domain Cobalt islands.
 R.D. Gomez, E.R. Burke, I.D. Mayergoyz, "Magnetic Imaging in the Presence of an External Field: Technique and Applications", J. Applied Physics 79, 6441-6446 (1996).
 R.D. Gomez, Quantification of magnetic force microscopy images by using combined electrostatic and magnetostatic imaging", J. Applied Physics 83, 6226-6228 (1998).
Follow this link to AIP to download the papers.