Researchers use light for thermomagnetic recording on a silicon waveguide

May 10, 2022

(News from Nanowerk) Researchers have demonstrated, for the first time, light-induced thermomagnetic recording in a magnetic thin film on silicon waveguides. The new writing technique is poised to enable high performance miniature magneto-optical memories that do not require bulky optics or mechanical rotation.

Magneto-optical storage devices combine magnetic and optical recording techniques to store information. Although several companies once manufactured rewritable magneto-optical disc drives, these drives are rarely used today.

“Despite their significant advantages, magneto-optical drives have been replaced by flash drives or cheaper optical storage media such as DVDs,” said research team leader Toshiya Murai of the Institute of Technology. from Tokyo to Japan. “Because our new recording method can be implemented using silicon photonics, it could enable inexpensive magneto-optical devices that store large amounts of information on a small chip.”

The researchers demonstrated light-induced thermomagnetic recording for the first time. The magnetic direction changes direction after light is coupled into the magnetic area of ​​the CoFeB magnetic film on the silicon waveguide. (Photo: Toshiya Murai, Tokyo Institute of Technology)

Researchers describe their novel magneto-topical memory devices and light-based writing technique in the journal Optica Publishing Group Express Optics (“Light-induced thermomagnetic recording of a CoFeB thin-film magnet on a silicon waveguide for on-chip magneto-optical memory”). The devices are non-volatile – meaning data is saved even when no power is supplied to the device – and can withstand many write and rewrite cycles.

Magneto-optical on-chip memories could provide all-optical alternatives to electronic packet routers used in today’s telecommunications infrastructure. “It would eliminate the energy and expense required for optical-electrical-optical conversions and enable flexible communication for each data packet,” Murai said. “Magneto-optical memories could also offer bit-level storage for optical computers, which use light to process, store, and transfer data.”

Controlling magnetism with light

Magneto-optical memory devices use heat to demagnetize a small spot on a magnetic film above a critical temperature known as the Curie point. A locally applied magnetic field then determines the direction in which the spot is magnetized as it cools. Achieving this type of thermomagnetic recording in a photonic integrated circuit requires controlling the magnetic state of a magnetic film inside a waveguide using light propagating in the waveguide. ‘wave.

In the new work, the researchers developed a way to use light propagating in the waveguide to reverse the magnetization direction by heating the magnetic recording film to near the Curie temperature. Their approach makes it easy to align the magnetization of the material in the direction of the applied external magnetic field.

To demonstrate the new technique, the researchers fabricated a silicon waveguide containing a thin-film magnet. Using a special high-resolution magneto-optical Kerr effect (MOKE) microscope, they were able to measure the magnetic properties of the film for different optical powers. This allowed them to show experimentally that the coercive force of the magnet on the silicon waveguide depends on the heat induced by the light guided in the waveguide.

“When the light was launched into the waveguide, we observed that the direction of magnetization would switch under an appropriate bias magnetic field,” Murai said. “Thus, we have demonstrated integrated light-induced thermomagnetic recording on a silicon photonics platform.”

Next, the researchers would like to develop magneto-optical solid-state recording systems that can not only write, but also read, information to a silicon photonics platform using the new method. This will require reducing the power consumption of light-induced thermomagnetic recording, which could be done by using a magnetic recording medium with a smaller volume combined with a shorter light pulse.


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