In searching for new ways to better control and understand magnetism, scientists at Texas A&M University have struck literal gold.
A recent study, led by chemists Matthew Sheldon and Dong Hee Son, has found that magnetic fields can be generated by shining a polarized beam of light on nanometer-sized particles of gold, a huge breakthrough in a decades-long global quest within the science community to identify techniques for ultrafast optical control of magnetism.
“We were able to lay a clear experimental ground that will enable the use of light to produce a controllable magnetic field without using ‘magnetic’ materials,” Son said. “I am very excited about this result.”
Gold in its bulk form traditionally has been classified as a typical diamagnetic material with weak magnetism, meaning it is unable to act as a magnet by itself. When the size of a gold sample is reduced to nanoscale, however, like many materials, it displays entirely different physical properties.
The team was able to show that, by manipulating their size and shape, gold nanoparticles will behave individually like small, albeit incredibly strong magnets when introduced to a controlled light source. Because the magnetic field only becomes charged under a light source, the magnetism can be turned off and on at ultrafast speeds — faster than one-trillionth of a second.
“Before starting these experiments, we published a manuscript of a theoretical study in which we outlined many of these predictions,” said Sheldon, a 2017 Gordon and Betty Moore Foundation Moore Inventor Fellow. “That said, we were unsure if it would actually be possible to measure the effect, because there was significant uncertainty about the magnitude of the magnetism and other assumptions in our theoretical analysis. It was very thrilling when we started collecting the data, and the signal was very clear, even stronger than we predicted.”
Sheldon notes that the magnetic field generated in their study is even greater than that of a refrigerator magnet and that its strength is directly proportional to the intensity of the incident light.
“Therefore, even stronger magnetic fields may be possible by further optimizing how the nanoparticles interact with light or by increasing the intensity of the incident light,” he said. “This could enable new technologies that need even stronger magnets.”
Gold nanostructures have generated widespread attention in recent years for their unique opto-electrical properties and increasingly have been utilized in many biomedical applications, including targeted drug therapy and diagnostics. Son notes that capitalizing on their magnetic features and the high-speed way in which they can be energized could have far-reaching impacts in the technological realm.
“Since magnetic fields can be generated with light, one may be able to replace the electrical current through the coils commonly used to produce magnetic fields with light propagating through space,” he said. “The contact-less control and much faster modulation of light intensity compared to the electrical current are definite advantages one can expect in future practical applications.”
For example, the technique could be used to implement significantly faster methods for saving data to the memory of a computer. Because magnets are used in the information-storing process, their size limits the memory capacities of current computer hard drives.
“The small, nanoscale size and the fast switching speed of the optically induced magnetism we observed could be used to overcome these limitations,” Sheldon said.
While gold has been an object of desire since the beginning of human existence, Sheldon says its true value is, now more than ever, becoming much more apparent. Among other directions, he hopes to measure the electrical current to determine if it could be used as an alternate way to generate electricity from light — a possible new strategy for solar energy.
“This result is just the first confirmation of many fascinating phenomena in this system, and we are continuing to explore the implications in my laboratory right now,” he added. “There are many significant scientific questions and impactful technologies based on these results that our laboratories will be exploring for years to come.”
The team’s research was funded in part by the Gordon and Betty Moore Foundation (Grant No. GBMF6882) and the Air Force Office of Scientific Research (Grant No. FA9550-16-1-0154), with additional support from the Welch Foundation (Grant No. A-1886) and Institute for Basic Science (Grant No. IBS-R026-D1).
The team’s paper, “‘Light-induced magnetism in plasmonic gold nanoparticles,” can be viewed online along with related figures and captions.
Learn more about Sheldon and his research group’s work with inorganic nanoscale materials at https://www.chem.tamu.edu/rgroup/sheldon/.
Learn more about Son and his research group’s work investigating the properties of organic and inorganic nanostructures at https://www.chem.tamu.edu/rgroup/son/.
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Contact: Chris Jarvis, (979) 845-7246 or firstname.lastname@example.org; Dr. Matthew Sheldon, (979) 862-3101 or email@example.com; or Dr. Dong Hee Son, (979) 458-2990 or firstname.lastname@example.org