Pioneering, Innovative Technique for Transforming Ambient Heat into Motion

An innovative method for converting ambient heat into motion in nanoscale devices has been devised by an international team of researchers. The method has the potential to significantly transform sensors as well as data storage in the future.

A new technique to transform ambient heat into motion in nanoscale devices has been created. Credit: University of Exeter

The pioneering research conducted by the international research team, including Professor Gino Hrkac from the University of Exeter, made a magnetic system with the ability to tap thermal energy by adopting a particular type of gear, or ratchet.

The thermal ratchet was produced using a material known as “artificial spin ice” it includes many tiny nanomagnets made of a nickel-iron alloy called Permalloy, the size of which is nearly 200 times lesser than the diameter of a strand of human hair.

The method can also be applied to transform magnetic energy into directed rotation of magnetization. Following magnetization of the sample, the team noted that the rotation of magnetization was in only one out of two directions. However, it was unclear why one direction was chosen over the other.

The research has been reported in Nature Materials, a leading scientific journal.

The system we have studied is an artificial spin ice, a class of geometrically frustrated magnetic materials. We were surprised to see that the geometry of the interactions can be tailored to achieve an active material that acts as a ratchet.

Sebastian Gliga, Marie Curie Research Fellow at the University of Glasgow, lead author of the research

Professor Gino Hrkac—a Royal Society Research Fellow from the University of Exeter, who is the second author of the study—said, “We tried to understand for quite some time how the system worked before we realized that the edges created an asymmetric energy potential.” This asymmetry can be observed through the magnetic field distribution at the nanomagnet array boundaries and makes the magnetization rotate in its chosen direction.

In order to image the evolution of the system’s magnetic state, the team adopted x-rays and the well-known magnetic dichroic effect. The measurements were conducted at the synchrotron light source SLS at the Paul Scherrer Institute, Switzerland, and at the Advanced Light Source, Lawrence Berkeley National Laboratory, United States.

Artificial spin ice has mainly been used to answer scientific questions, for example concerning the physics of frustration. This is a nice demonstration of how artificial spin ice can be a functional material and provides a step towards applications.

Professor Laura Heyderman, ETH Zurich and Paul Scherrer Institute

The results of the study have set up an unprecedented course to converting magnetic energy into the directed rotation of magnetization.

The impact observed in the two-dimensional magnetic structures at present looks promising that it can potentially be used in nanoscale devices, for example, actuators, magnetic nanomotors, or sensors.

In fact, since angular momentum is conserved and spin is a form of angular momentum, the variation in the system’s magnetic moment has the ability to generally cause a physical rotation of the system via the Einstein–de Haas effect. It can also be used in magnetic memory in which bits can be stored by carrying out local heating using laser pulses.

The paper titled ‘Emergent dynamic chirality in a thermally driven artificial spin ratchet’ has been published in the journal Nature Materials.

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 funded the study.

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