Indian duo discover new `frustrated magnet’

The work, which would greatly benefit a number of future studies in basic research, was published recently in two of the most prestigious international journals — Nature and Physical Review Letters.

Carried out by B Sriram Shastry and Rahul Siddharthan of Indian Institute of Science (IISC) together with scientists from Bell Laboratories, Princeton University and Argonne National Laboratory, USA, the work introduces a new set of compounds in a novel class of frustrated magnet called spin ice.

There exists compounds in nature having properties idealised by spin ice– magnetic analogue of water ice — which can be used to test low temperature behaviour of materials.

Spin ice compounds have relevance to understand glasses and freezing, Shastry said.

Called pyrochlore, the new spin ice class of compound (rare earth titanates) would assist in studying magnetic ordering versus frustration, he said. The Indian side provided the theoretical support whereas the experiments were conducted in USA.

"The work gives an example of a system which can be cooled down to much lower temperatures than ice, to a few degrees Kelvin (water freezes at 273 degrees Kelvin), without any development of magnetic ordering," Shastry said.

The real importance of the work lies in the fact that the compounds are shown to have ground states with a finite entropy (a measure of molecular disorder of a system) by measuring the low temperature specific heat.

The study of magnetic frustration was not much advanced due to difficulties in isolating the frustration from other perturbations caused bydefects in magnetic materials.