Researchers at The University of Manchester facilitate the development of advanced magnetic materials
Even without noticing this, everyday we all make use of many magnetic gadgets and devices, both at home and at work. There are dozens of magnets working in our cars and household appliances and billions of tiny magnets keep records on computer hard disks. These are just a few examples of the importance of magnetic materials in supporting our modern lifestyle.
Whether a particular material can be used in a simple appliance, such as an electric bell, or can be a part of a sophisticated electronic memory device depends crucially on how regions with different orientations of magnetic moments (simply speaking, regions having magnetic fields in either south or north pole directions) propagate through the material. These regions are called magnetic domains and boundaries between them – usually many atomic layers thick – called domain walls (see photos).
Materials where domain walls can easily move back and forth are good for electric transformers and electronic circuits. In the opposite case, where domain walls are pinned by defects and cannot move at all, a material would be a primary choice for horseshoe magnets and electric motors. Therefore, it is hardly surprising that movements of domain walls have been intensively studied since early days of the physics of magnetism (more than a century ago), which contributed greatly to the creation of better and better magnetic materials.
Now researchers at Manchester University have managed to reach the ultimate level of resolution with which it is possible to detect (or even think about) domain wall movements.
In a forthcoming article in Nature (issue of 18/25 December, 2003), Professor Andre Geim from The University of Manchester and his colleagues Dr K. Novoselov, Dr S. Dubonos, Dr E. Hill & Dr I. Grigorieva report how domain walls move on a scale smaller than the distance between neighbouring atoms in a material. The researchers discovered that at this scale domain walls no longer roll smoothly through the crystal but rather jump between adjacent rows of atoms, having to overcome a small barrier at each row. In effect, their motion reminds a ball rolling on a washboard. This ‘hurdle racing’ of domain walls was first predicted before WWII by British physicist Rudolf Peierls but, despite many earlier attempts, the phenomenon has until now eluded experimental detection. “If we were interested in entering the Guinness book, this record would stay there forever”, quips Professor Geim.
According to the researchers, their results are much more than just a record. Rather, they lead to better understanding of fundamental and technologically important phenomena governed by movements of domain walls and will facilitate the development of advanced magnetic materials.
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