Using a specially engineered beam of light from an ultrafast laser, UC San Diego engineers demonstrate a new approach to switch magnetic information in materials without using an external magnetic field. [Image: David Baillot, UC San Diego Jacobs School of Engineering]
In the ongoing quest to improve data storage, all-optical switching could be much faster and more energy-efficient than traditional external magnetic field switching. Limitations on the thickness of magnetic material and precise polarization requirements, however, have placed constraints on making the method practical.
Now, researchers at a US university have shown how a shaped and focused light beam can control magnetic bits in multilayered materials with no external magnetic field (Nat. Commun., doi:10.1038/s41467-026-77572-3 ). The work could lead to optical switches more than three orders of magnitude faster than their magnetic counterparts.
Shaping the light
Electrical engineering professor Abdoulaye Ndao and his colleagues at the University of California San Diego combined high numerical aperture optics and structured-light illumination to create circularly polarized vector beams of light. Such beams retain the transverse polarization component of the light while suppressing the longitudinal component at the focal point of the experimental system. They also concentrate the light into a smaller spot size, delivering more energy per unit area to the magnetic material.
A specially designed optical system (foreground) shrinks, shapes and concentrates light from a femtosecond laser (left) in order to produce optical switching in a magnetic material. UC San Diego doctoral students Koffi Sadzi (left) and Muhammad Waleed Khalid (right) adjust the optical setup for their experiments. [Image: David Baillot, UC San Diego Jacobs School of Engineering]
The optical path started at a Ti:sapphire laser, producing 120-fs pulses at a wavelength of 800 nm. An iris narrowed the beam, which then passed through optical components including a half-wave plate,
polarizer, S-waveplate and vortex phase plate to structure the circular polarization. Two mirrors combined the vector beams with LED illumination before objectives focused the light onto the target material.
For the magnetic material, Ndao’s team created stacks of thin, alternating layers of platinum and cobalt, supported by a glass substrate. Up to nine layers worked well, while previous efforts without the circularly polarized vector beams were limited to three layers of material.
Concentrating the light on a small spot—ranging from 1.92 to 0.96 μm—heated the material, thus altering its electrical state. Below a spot size of roughly 1.36 μm, the magnetic reversal becomes independent of the helicity of the polarization.
Future prospects
“Instead of designing a new material to enable optical switching, we redesigned the light itself and showed new properties that were not previously thought to be possible,” Ndao said in a statement.
Future investigations may involve testing other materials for their responses to shaped light, narrowing the beam’s width to a spot a few hundred nanometers across, and trying other pulsed lasers that could fit better in an optoelectronic storage device.
