Magnetic monopoles perform a random walk

In this week’s edition of Nature Communications, Dr. Laura Bovo and co-workers at the London Centre for Nanotechnology (LCN) and the University of Oxford report experimental evidence that magnetic monopoles in spin ice undergo a random wandering motion analogous to the “Brownian” motion of pollen grains in water, first observed by Thomas Brown in 1827.

Emergent magnetic monopoles - the magnetic variant of a charged particle such as an ion, electron or proton – have been a significant recent discovery in the field of fundamental magnetism. In previous studies, Prof. Steve Bramwell (LCN) and his collaborators demonstrated the existence of these monopoles in a special material called "spin ice" and observed their currents in a magnetic version of electricity, or "magnetricity".

The experiments performed by Bovo and colleagues on the spin ice material Dy2Ti2O7 suggest that the overall Brownian motion of magnetic monopoles is underpinned by monopoles hopping from point to point, in a quantum mechanical “tunnelling” process.

The researchers achieved this insight by measuring the response of the material to a magnetic field oscillating at acoustic frequencies.

Professor Steve Bramwell says “This is the first step to understanding how magnetic monopoles get from A to B. If we can understand that, then we are closer to harnessing the motion of magnetic monopoles to useful ends such as low power data processing.” 

Journal Link: Brownian motion and quantum dynamics of magnetic monopoles in spin ice - doi:10.1038/ncomms2551

Figure: "Brownian motion and quantum dynamics of magnetic monopoles in spin ice: A schematic representation". Blue (red) circles represent negative (positive) monopoles hopping from point to point, in a quantum mechanical “tunnelling” process (green arrow) – the overall Brownian motion (red/blue stripes) resemble that of a random walk.

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LCN Author(s): 
Other contributors: 
D. Prabhakaran