A magnetic charge can behave and interact just like an electric charge in some materials, according to new research led by the London Centre for Nanotechnology (LCN). The findings could lead to a reassessment of current magnetism theories, as well as significant technological advances. The research, published in Nature, proves the existence of atom-sized ‘magnetic charges’ that behave and interact just like more familiar electric charges. It also demonstrates a perfect symmetry between electricity and magnetism – a phenomenon dubbed ‘magnetricity’ by the authors from the LCN and the Science and Technology Facility Council’s ISIS Neutron and Muon. In order to prove experimentally the existence of magnetic current for the first time, the team mapped Onsager’s 1934 theory of the movement of ions in water onto magnetic currents in a material called spin ice. They then tested the theory by applying a magnetic field to a spin ice sample at a very low temperature and observing the process using muons at ISIS. The experiment allowed the team to detect magnetic charges in the spin ice (Dy2Ti2O7), to measure their currents, and to determine the elementary unit of the magnetic charge in the material. The monopoles they observed arise as disturbances of the magnetic state of the spin ice, and can exist only inside the material.Professor Steve Bramwell, LCN co-author of the paper, said: “Magnetic monopoles were first predicted to exist in 1931, but despite many searches, they have never yet been observed as freely roaming elementary particles. These monopoles do at least exist within the spin ice sample, but not outside. “It is not often in the field of physics you get the chance to ask ‘How do you measure something?’ and then go on to prove a theory unequivocally. This is a very important step to establish that magnetic charge can flow like electric charge.
It is in the early stages, but who knows what the applications of magnetricity could be in 100 years time.”Professor Keith Mason, Chief Executive of STFC said: “The unequivocal proof that magnetic charge is conducted in spin ice adds significantly to our understanding of electromagnetism. Whilst we will have to wait to see what applications magnetricity will find in technology, this research shows that curiosity driven research will always have the potential to make an impact on the way we live and work. Advanced materials research depends greatly on having access to central research labs like ISIS allowing the UK science community to flourish and make exciting discoveries like this.”Dr Sean Giblin, instrument scientist at ISIS and co-author of the paper, added: “The results were astounding, using muons at ISIS we are finally able to confirm that magnetic charge really is conducted through certain materials at certain temperatures – just like the way ions conduct electricity in water.” Four papers – two published in Science this week, and two on the preprint archive – independently present evidence that magnetic monopoles really exist in nature. Two of these papers were written by London Centre for Nanotechnology (LCN) scientists.To find a magnetic monopole is a Holy Grail of physics. A magnetic monopole is the magnetic version of a charged particle like an electron, and for the last 70 years physicists have believed that one might exist somewhere in the universe. The monopoles discovered this week are not that Holy Grail, but are the next best thing. Rather than existing throughout the universe, they only exist within a special type of material called `spin ice’. They can be imagined as the north and south poles of magnets, but free to float around independently within the material. However, someone living within in a block of spin ice would think that these are exactly those magnetic monopoles long sought by physicists.
The first LCN paper by Fennell and colleagues is a collaboration between the LCN, the Institute Laue Langevin (ILL), Grenoble, and Oxford University. It uses a special neutron scattering technique to image the world in which the monopoles inhabit. This was made possible by recent improvements to experimental instruments at the ILL, funded in part by the U.K. The second LCN paper by Professor Steve Bramwell and Colleagues is a collaboration between LCN, ISIS and Oxford. ISIS is another U.K. facility that in this case was used to produce subatomic particles called muons that were then used as a probe for the monopoles. In this experiment the charge of the monopole was directly measured and found to be equal to that predicted by theory.Evidence for magnetic monopoles in spin ice – the bottom row shows predicted neutron scattering data and above is the real data gathered at the ILL, using experimental apparatus that was recently improved by UK funding (the so-called Millenium Programme).“These recent papers provide overwhelming proof of the existence of magnetic monopoles in spin ice,” says Prof. Steve Bramwell of the LCN, ”in particular we have measured the monopole charge and observed monopole currents analogous to electricity. We have also used neutrons to measure the length of the so-called Dirac strings that run between North and South monopoles. ”The research shows how certain real materials, in this case spin ice, create within themselves things that resemble the basic particles by which the universe is composed. “The amazing thing about spin ice monopoles” continues Prof. Bramwell, “is how perfect they are: they really do look just like those monopoles expected to exist somewhere in the universe. Why nature should reproduce a mini-universe within a material, we do not yet know”.As well as having implications for fundamental physics, the monopoles could be harnessed in the way that electrical charges are, for technology. “A magnetic version of electricity is a long way off” says Prof. Bramwell, “but these results are an important first step”. news from sciencedaily.com & london-nano.com
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