Light and magnetism have been used for centuries to measure objects, from Earth’s mass to the tiny optical lens sensors embedded in smartphones. In fact, Faculty of Science physicist Paul Barclay calls laser light the world’s best "ruler."
But as objects get smaller and smaller — to the nanoscale size (about 100 times smaller than the width of a human hair) — measuring their movement with extreme precision and high sensitivity becomes increasingly difficult.
Now, in a unique collaboration, Barclay’s team of physicists at the University of Calgary and University of Alberta physicist Mark Freeman and his research group have shown for the first time that a nanosized device — called an optical-mechanical resonator (or optical cavity) — can be used to measure the magnetic properties of an even smaller object placed on the device. The two teams built and tested their nanophotonic optomechanical device at the National Institute of Nanotechnology’s (NINT) and the nanoFAB facility at the U of A.
Their paper, “Nanocavity Optomechanical Torque Magnetometry and Radiofrequency Susceptometry,” is published in Nature Nanotechnology, a peer-reviewed journal in the top-ranked Nature series.
Device the first to measure nanomagnetics at high sensitivity
“This is the first demonstration, using nanophotonics technology, to probe nanomagnetism or any other related microscopic phenomena,” says Barclay, associate professor of physics and astronomy and Alberta Innovates Scholar in Quantum Nanotechnology in the Faculty of Science.
“This device is the first of its kind in the world, because we’ve shown it can be useful to measure nanomagnetics at high sensitivity, in ambient conditions, and we can actually probe a property with this sensitivity,” he notes.
Along with providing fundamental insights into nanomagnetic phenomena, the research could lead to applications ranging from highly sensitive sensors and enhanced magnetic storage of computer information, to a "laboratory-on-a-chip" for analyzing materials in any nanoscale condensed matter system.
“This is a really key step — maybe the biggest step — toward making a practical lab-on-a-chip for studying small magnetic specimens that hopefully can become truly practical, could be mass-produced and be adopted in lots of applications where knowing the magnetic properties is important,” says Freeman, professor of physics and Canada Research Chair in condensed matter physics at the U of A, and research officer at NINT.
Collaboration crucial to success
Barclay’s research group is part of the University of Calgary’s Institute for Quantum Science and Technology and NINT.
The new device couples his team’s expertise in sculpting nanosized optomechanical resonators with the Freeman team’s pioneering work in torque magnetometry. This involves integrating magnetic material on miniaturized sensors, turning on a magnetic field to create a magnetic torque or movement in the sensors, and then measuring the magnetics data.
“If we put an object, like a nanoscale particle, onto our optical cavity, that induces torque on the object which then causes it to move. We’re able to very sensitively detect that torque and measure that movement really well,” Barclay says.
Freeman says the new device is a thousand times more sensitive than what was possible before. “When you combine this really sensitive nanocavity readout that Paul’s group has developed, with the nanomechanical sensors that my group had developed, then the whole technique just gets so much better.”
Barclay and Freeman say the achievement wouldn’t have been possible without the two teams working closely together and the investment in NINT and the nanoFAB.
“The collaboration was critical. This work simply wouldn’t have happened without it — even the conception of the idea,” Barclay says.
Agrees Freeman: “It was really a great collaboration where you have two groups that have very distinct different strengths, but where both of those strengths are required at a high level to actually get the project done.”
Students, postdocs built and measured the device
Students and postdoctoral scholars on Barclay’s and Freeman’s teams led in building and measuring the new device.
From Barclay’s group, PhD student Marcelo Wu and postdoc Nathanael L.-Y. Wu worked closely at NINT and the nanoFAB with postdoc Joseph Losby from Freeman’s group to combine the intricate, silicon-based optical cavity with a thin, metal nanodisk of magnetic material, and to develop the apparatus for measuring the magnetic properties.
From Freeman’s team, PhD student Tayyaba Firdous collected most of the data, while PhD student Fatemeah Fani Sani ran computer simulations to verify the data.
The research was supported by the Natural Science and Engineering Research Council of Canada, Canada Research Chairs, the Canada Foundation for Innovation, and Alberta Innovates.