Scientists Transform Heat Into Motion

By Chemical Processing Staff

Oct 25, 2017

A team of scientists reportedly find a new way to transform ambient heat into motion in nanoscale devices – a discovery that could open up new possibilities for data storage, sensors, nanomotors and other applications, according to the University of Glasgow. In a new paper published in the journal Nature Materials, an international team of researchers from institutes including the University of Glasgow and the University of Exeter in the U.K. and from the ETH Zurich and the Paul Scherrer Institute in Switzerland describe how they created a magnetic system capable of extracting thermal energy on the nanoscale, using the concept of a gear known as a ratchet, and turning magnetic energy into the directed rotation of the magnetization. 

The thermal ratchet was realized in a material known as “artificial spin ice” made of an assembly of tiny nanomagnets of Permalloy, a nickel–iron alloy. The individual nanomagnets are just 470 nanometres long (or about 200 times smaller than the diameter of a human hair) and 170 nanometers wide, with only a single magnetic domain; that is, the magnetization can only point in one of two directions along the long axis of the magnet. After magnetizing their sample, the researchers observed that the magnetization rotated in only one of two possible directions. Without an obvious reason why, one way should be preferred over the other, according to the university.

“The system we have studied is an artificial spin ice, a class of geometrically frustrated magnetic materials,” says Sebastian Gliga, the lead author of the study and Marie Curie Research Fellow at the University of Glasgow. “We were surprised to see that the geometry of the interactions can be tailored to achieve an active material that exhibits dynamic chirality and thus acts as a ratchet.”

The findings reportedly establish an unexpected route to transforming magnetic energy into the directed motion of magnetization. The effect now found in the two-dimensional magnetic structures comes with the promise that it will be of practical use in nanoscale devices, such as magnetic nanomotors, actuators or sensors. Because angular momentum is conserved and spin is a type of angular momentum, the change in the magnetic moment of the system can in principle induce a physical rotation of the system. It may also find applications in magnetic memory where bits could be stored through local heating with laser pulses.

The work was funded by the European Union’s Horizon 2020 research and innovation program, the Engineering and Physical Sciences Research Council (EPSRC), the Vienna Science and Technology Fund and the Royal Society.

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