Pretty magnetic monopoles

05/08/2010

Pick of the pics

A pretty magnetic pattern is pretty surprising too

Against the rules, triplets of magnetic north poles (bright points) and south poles (dark points) chum together with amazing regularity on small islands etched in a honeycomb pattern on an iron surface, using an electron beam. Hartmut Zabel at the Ruhr-Universität Bochum calls it a new magnetic order. The polarities are revealed by a magnetic force microscope, and the 20-micrometre scale line tells us that the width of the picture is about the average thickness of a human hair. Credit: RUB

Who’d have thought it? In kindergarten science you learn that like magnetic poles repel each other. Yet here we see energetically unfavourable triplets of poles occurring not just once or twice by mistake but all across a specially prepared iron surface, when subjected to a magnetic field.

The so-called “magnetic monopoles” created in this pattern are not to be confused with hypothetical fundamental particles of that name. And be wary of attempts to explain the phenomenon to you by reference to “spin ice”, and an analogy with water ice. They may be helpful for experts but can baffle non-physicists. All you really need to know is that the exposed north or south poles belong to atoms that can face one way or the other on the lattice surface.

Watch out for novel information-storage devices exploiting this “new magnetic order”. Prof. Zabel points out that “each node point has eight possible dipole constellations – far more than with conventional storage techniques based on two states”. The islands in the experiments were 3 micrometres long, but they might be made ten times smaller.

References

Alexandra Schumann, Björn Sothmann, Philipp Szary and Hartmut Zabel, “Charge ordering of magnetic dipoles in artificial honeycomb lattices,” Applied Physics Letters, Vol. 97, 022509 (2010). doi:10.1063/1.3463482

RUB press release: http://www.alphagalileo.org/ViewItem.aspx?ItemId=82499&CultureCode=en

For a relevant report last year from Helmholtz-Zentrum Berlin für Materialien und Energie see http://www.sciencedaily.com/releases/2009/09/090903163725.htm