A team from the UK and France used Dy2Ti2O7, a material known as a spin ice, to test the new technique. Spin ices are predicted to have sharply defined magnetic point charge (magnetic monopole) excitations, making them good test materials.
In their recent paper, the researchers explained how they applied Onsager's theory of electrolytes, which describes the conductivity of liquid and lattice electrolytes, to set up an experiment that can detect the magnetic monopoles in spin ice. They replaced the electrical quantities described in Onsager's theory with magnetic quantities, based on the assumption that there is equivalence between electricity and magnetism.
A spin ice sample was cooled to temperatures close to zero and then probed using muons, negatively charged elementary particles. Single crystals of spin ice were aligned parallel to the muon spin direction and a magnetic field was applied at right angles to this axis. The asymmetry of muon beta decay was then measured as a function of time, leading to information on internal magnetic fields.
Results so far have yielded a value of 5 μB Å−1 for the elementary unit of magnetic charge. The technique has not only been used to prove the existence of magnetic charges in spin ice but is also capable of measuring relative changes in magnetic conductivity. While the new technique is a good proof of theory, can be used to determine deviations from Ohm's law, and demonstrates good correlation between electricity and magnetism, it may also lead the way to controlling magnetic charges in the future.