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Finally, A Spin Wave Is Observed in A Two-dimensional Magnet

wallpapers Tech 2020-08-28

Discovery of Spin Waves in Two-dimensional Magnets

Just like the Bigfoot and Loch Ness monsters, the critical "spin wave" in the magnetic system has not yet been captured, photographed and caught. Unlike the legendary creatures, these highly correlated electron spin pattern fluctuations do exist, but they are too random and turbulent to be seen in real time. A research team at Cornell University has developed a new imaging technique that is fast and sensitive enough to observe these elusive critical fluctuations in a two-dimensional magnet.
The authors of the study are Mai Jianhui, associate professor of physics in the School of Arts and Sciences, and Shan Jie, professor of applied and engineering physics in the School of Engineering. Both researchers are members of the Kavli Institute of Nanoscience at Cornell University. The Nanoscience and Microsystem Engineering (NEXT Nano) initiative came to Cornell University, where its shared laboratory specializes in atomically thin quantum materials.
When the magnetization fluctuation occurs near the thermodynamic critical point, it is considered "critical". The thermodynamic critical point refers to the moment when a substance transforms into a new phase state, resulting in various unusual phenomena. In this critical area or critical point, fluctuations are no longer random behaviors, but become highly correlated.

Capture Fluctuations in Real Time

This is what happens when the fluctuations become correlated, which can cause dramatic effects in a system and on any scale, because this correlation can theoretically reach infinity, and the fluctuations seen in research are spin or magnetic moments. Fluctuations. These critical magnetization fluctuations are difficult to see because they are constantly changing and occur in a very narrow temperature range.
There are still many challenges in observing signals from a single atomic layer. The researchers used a single-layer ferromagnetic insulator, chromium bromide, as a two-dimensional system, which has a wider critical region and stronger fluctuations. In order to see these fluctuations in real time, researchers need an equally fast method with high spatial resolution and wide-field imaging capabilities.
The ability to capture this phenomenon in real time means that researchers only need to apply a small voltage to switch the fluctuations back and forth between different states to control the critical fluctuations in the magnet. Once the target state or value is reached, the voltage can be turned off. No magnetic field is needed to control the fluctuations because they are essentially self-driven. This is a fundamentally different concept from active magnetic state switching because it is completely passive. This is a switching based on information obtained from measurements, rather than an active drive system. So this is a new concept that can save a lot of energy.