A new material can act as a super-fast magnetic switch so when it ends up struck by successive ultra-short laser pulses it exhibits “toggle switching” that could increase the capacity of the global fiber optic cable network by an order of magnitude.

Switching between two states – 0 and 1 – is the basis of digital technology and the backbone of the Internet. The vast majority of all the data downloaded ends up stored magnetically in huge data centers across the world, linked by a network of optical fibers.

Obstacles to further progress with the Internet are three-fold, specifically the speed and energy consumption of the semiconducting or magnetic switches that process and store our data and the capacity of the fiber optic network to handle it.

The new discovery of ultra-fast toggle switching using laser light on mirror-like films of an alloy of manganese, ruthenium and gallium known as MRG could help with all three issues, said researchers at CRANN and the School of Physics at Trinity College Dublin.

Not only does light offer a great advantage when it comes to speed but magnetic switches need no power to maintain their state. More importantly, they offer the prospect of rapid time-domain multiplexing of the existing fiber network, which could enable it to handle ten times as much data.

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Working in the photonics laboratory at CRANN, Trinity’s nanoscience research center, Dr. Chandrima Banerjee and Dr. Jean Besbas used ultra-fast laser pulses lasting just a hundred femtoseconds (one ten thousand billionth of a second) to switch the magnetization of thin films of MRG back and forth. The direction of magnetization can point either in or out of the film.

With every successive laser pulse, it abruptly flips its direction. Each pulse is thought to momentarily heat the electrons in MRG by about 1,000 degrees, which leads to a flip of its magnetization.

Dr. Karsten Rode, senior research fellow in the ‘Magnetism and Spin Electronics Group’ in Trinity’s School of Physics, said the discovery just marks the beginning of an exciting new research direction.

Researchers Dr. Chandrima Banerjee and Dr. Jean Besbas at CRANN and Trinity College Dublin’s School of Physics discovered a new material can act as a super-fast magnetic switch.
Source: CRANN, and Trinity College Dublin


“We have a lot of work to do to fully understand the behavior of the atoms and electrons in a solid that is far from equilibrium on a femtosecond timescale,” Rode said. “In particular, how can magnetism change so quickly while obeying the fundamental law of physics that says that angular momentum must be conserved?

“In the spirit of our spintronics team, we will now gather data from new pulsed-laser experiments on MRG, and other materials, to better understand these dynamics and link the ultra-fast optical response with electronic transport. We plan experiments with ultra-fast electronic pulses to test the hypothesis that the origin of the toggle switching is purely thermal.”

Next year, Chandrima will continue her work at the University of Haifa, Israel, with a group who can generate even shorter laser pulses.

Trinity researchers, led by Karsten, plan a new joint project with collaborators in the Netherlands, France, Norway and Switzerland, aimed at proving the concept of ultra-fast, time-domain multiplexing of fiber-optic channels.

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