Magnetism’s noise can now be measured to improve magnetic spin

The level of noise associated with the propagation of magnon current, quasi-particles associated with waves of magnetization, has been measured, and this could help the development of magnonic computers.

A microchip that generates a magnonic current between transmitting and receiving antennae was created by electrical and computer engineering researchers at the University of California Riverside’s Marlan and Rosemary Bourns College of Engineering. A magnonic current is the transfer of a magnetic spin, where quasi-particles, called magnons, propagate that spin, passing through a material, a circuit, to deliver a signal. This quasi-particle propagation is also called a spin wave. The researchers measured the magnon current noise in this transmitting and receiving antennae, microchip system. Noise, or fluctuations in a current’s flow, is important in determining if an electronic device can be used in practice.

This diagram shows how the same spin is transferred from particle to particle by the magnon current of quasi-particles. Credit: Alexander Balandin

“One can say that the noise of magnons is discreet at low power but becomes high and discrete at a certain threshold of power,” said University of California (UC), Riverside professor of electrical and computer engineering professor, Alexander Balandin. “This constitutes the discreet charm of the magnonic devices. Our results also tell us possible strategies for keeping the noise level low.”

Low power computation

The first experimental devices have been relatively large, and the next step is to investigate the physical mechanisms of magnon noise. Balandin’s team plans to test a much smaller version of a magnon device. For now, his research group is experimenting with generic components to understand the fundamentals of magnon current noise.

Balandin has concluded so far that: “Magnonic devices should be preferably operating with low-power levels.” Magnons are not true particles like electrons and do not generate as much heat as they pass through a material; but they behave like particles and can be treated as such. Electrons, which are also noisy, are not needed.

Experiments revealed that magnons are not that noisy at low-power levels, but at high-power levels, the noise became dominated by broad fluctuations which researchers called random telegraph signal noise that would interfere with a device’s performance. The noise was noticeably different from that made by electrons and identifies limitations on how to build magnonic devices.

Existing electronics have metals or semiconductors and electrons move through these materials and the materials electrical resistance leads to heating and energy dissipation. As devices have become smaller, the higher density of transistors accelerates this energy loss from heating. Devices that use these conventional electronic currents may not be able to become smaller because of this heat and its impact on the circuit. Magnonic devices are not expected to have this problem with miniaturisation.

The work was supported as part of Spins and Heat in Nanoscale Electronic Systems, an Energy Frontier Research Center at UC Riverside funded by the United States’ Department of Energy, Office of Science, Basic Energy Sciences.