Spin ice route to monopoles, ‘magnetricity’

Various : A series of papers in Science and Nature report new results on spin ices and monopoles. The Nature paperSpin ices are an exotic class of crystalline solids that are rare, three-dimensional systems in which the magnetic moments (spins) of the ions remain disordered even at the lowest temperatures available writes Shivaji Sondhi in Nature. This means that the geometrical layout of the atoms are such that the norths and souths are never able to align in a satisfactory way and so the magnets continually flip up and down trying to find a stable position says Hannah Delvin in the London Times .The material has a second property, at regular intervals on the lattice the magnetic fields of individual atoms add up to produce essentially isolated north or south charges, behaving as point-like objects that are the condensed-matter versions of Paul Dirac’s theoretical magnetic monopoles —particles that, unlike iron magnets, have a single magnetic pole and hence carry an overall magnetic charge.Initially, it was not evident that their charge could be measured in a straightforward way. Magnetic monopoles live in a lattice at a moderate density under normal laboratory conditions—not the sort of setting in which you could carry out a magnetic version of Millikan and Fletcher’s oil-drop experiment to determine the electric charge of the electron.But Steve Bramwell of the London Centre for Nanotechnology and colleagues in Nature report a measurement of the magnetic charge of the monopoles in spin ice that is in surprisingly good agreement with the theoretical prediction."It is not often in the field of physics you get the chance to ask, âHow do you measure something?’, and then go on to prove a theory unequivocally,” said Bramwell to Delvin . “This is a very important step to establish that magnetic charge can flow like electric charge.” The Science papersIn Science, two groups also report measurements from neutron-scattering experiments showing that the low-energy excitations in spin ices are reminiscent of magnetic monopoles writes Michel J. P. Gingras .These dissociated north and south poles diffuse away from each other in these oxides and leave behind a " Dirac string ” of reversed spins that can be seen as patterns in the intensity of scattered neutrons. Related Links Discovery of âmagnetricity’ marks important advance in physics London Times Measurement of the charge and current of magnetic monopoles in spin ice Nature Observing Monopoles in a Magnetic Analog of Ice Science Magnetic Coulomb Phase in the Spin Ice Ho ₂Ti ₂O ₇ Science Dirac Strings and Magnetic Monopoles in the Spin Ice Dy ₂Ti ₂ Science