Uncovering The Secrets Of Ultralow Power Electronics

Researchers are now closer to understanding the unique properties of topological insulators, materials which could be used in low power electronic devices.

AsianScientist (Jan. 8, 2016) – In exotic materials known as topological insulators, non-magnetic elements act as a glue to help align atomic magnets in the same direction. These findings, published in Nature Communications, could help develop ultralow power consumption electronic devices.

“Hopefully, this achievement will lead to the creation of novel materials that operate at room temperature in the future,” said Akio Kimura, a professor at Hiroshima University and a member of the research group.

Their achievement can be traced back to the discovery of the quantum Hall effect in the 1980’s, where an electric current flows along an edge (or interface) without energy loss. However, this requires both a large external magnetic field and an extremely low temperature, limiting practical applications. Researchers believed that this problem could be overcome with new materials called topological insulators that have ferromagnetic properties such as those found in Cr-doped (Sb, Bi)2Te3.

A topological insulator, predicted in 2005 and first observed in 2007, is neither a conductor nor an insulator. They exhibit exotic properties, for example, only generating electric currents at the surface or the edge of the material, while no electric current is generated inside it.

At extremely low temperatures, an electric current flows around the edge of the Cr-doped (Sb, Bi)2Te3 thin films without energy loss and without an external magnetic field. Despite the attractiveness of these unique ferromagnetic properties, scientists do not fully understand the mechanism by which this occurs.

Because Cr is a magnetic element, a Cr atom is equivalent to an atomic-sized magnet. The N-S orientations of such atomic-sized magnets tend to be aligned in parallel by the interactions between the Cr atoms.

When the N-S orientations of Cr atoms in Cr-doped (Sb, Bi)2Te3 are aligned in parallel, the material exhibits ferromagnetism. However, the interatomic distances between the Cr atoms in Cr-doped (Sb, Bi)2Te3 are, in fact, too long to interact sufficiently to make the material ferromagnetic.

Kimura and his team found that the non-magnetic element atoms, such as the Sb and Te atoms, mediate the magnetic interactions between Cr atoms and serve as the glue to fix the N-S orientations of Cr atoms to face one direction. In addition, the group expects that its finding will provide a way to increase the critical temperature for relevant device applications.

The article can be found at: Ye et al. (2015) Carrier-Mediated Ferromagnetism in the Magnetic Topological Insulator Cr-doped (Sb,Bi)2Te3.

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Source: Hiroshima University.
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