Monopoles and magnetricity - the story of spin ice
12 Jan 2011 by Evoluted New Media
A major breakthrough has been made in understanding magnetic monopoles and magnetricity as scientists have created artificial spin ice in a state of thermal equilibrium for the first time.
A major breakthrough has been made in understanding magnetic monopoles and magnetricity as scientists have created artificial spin ice in a state of thermal equilibrium for the first time.
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Structure of spin ice Credit Nature Physics/Jason P. Morgan, Aaron Stein, Sean Langridge and Christopher H. Marrows. |
Scientists have been able to probe spin ice – a nanomaterial consisting of millions of tiny magnets – in minute detail and have studied the phenomenon of magnetic monopoles within the structures.
“Spin ices have created a lot of excitement in recent years as it has been realised that they are a playground for physicists studying magnetic monopole excitations,” said Dr Christopher Marrows from the University of Leeds.
The spin ice is built up using nanotechnology with the magnets existing in a ‘frustrated’ lattice structure – all the interactions between the atoms cannot be satisfied at the same time. Magnetic dipoles with a north and south pole are arranged in tetrahedron structures – each dipole has a magnetic moment which attract and repel each other, so the dipoles are forced to arrange themselves into the lowest possible energy state, two poles in and two poles out.
“All of the samples of these artificial structures created in the lab have been what we called jammed,” Marrows said, “What we have done is find a way to un-jam spin ice and get it into a well-ordered ground state known as thermal equilibrium.”
Marrows said that once in this state the sample can be frozen and observed to see which way all the little magnets are pointing.
“Getting the sample to self-order in such a way has never been achieved experimentally before and for a while had been considered impossible,” said lead author Jason Morgan, “But when we looked at the sample using magnetic force microscopy and saw this beautiful periodic structure we knew instantly that we had achieved an ordered ground state.”
Scientists were able to observe individual excitations out of the ground state which they say is evidence from monopole dynamics within the lattice. They hope to understand these monopoles and advance a novel technology field known as magnetricity.
