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Diamonds show promise for spintronic devices

Researchers at American Institute of Physics (AIP) and La Trobe University have been exploring the potential of technology called spintronics, which they believe could lead to new types of more efficient and powerful devices.

Researchers have been exploring the potential of technology called spintronics, which they believe could lead to new types of more efficient and powerful devices.

According to the team, spintronics relies on detecting and controlling a particle's spin, rather than the electric charge.

In a paper published in Applied Physics Letters, from AIP Publishing, researchers measured how strongly a charge carrier's spin interacts with a magnetic field in diamond, claiming that this crucial property demonstrated diamond as a promising material for spintronic devices. The belief is that diamond would be easier to process and fabricate into spintronic devices than typical semiconductor materials.

Conventional quantum devices are based on multiple thin layers of semiconductors, which require an elaborate fabrication process in an ultrahigh vacuum.

Diamond is a good insulator, but when this material is exposed to hydrogen plasma, it apparently incorporates hydrogen atoms into its surface. When a hydrogenated diamond is introduced to moist air, it becomes electrically conductive because a thin layer of water forms on its surface, pulling electrons from the diamond. The missing electrons at the diamond surface are said to behave like positively charged particles, known as holes, making the surface conductive.

These holes are said to have many of the right properties for spintronics. The most important is apparently a relativistic effect called ‘spin-orbit coupling’, where the spin of a charge carrier interacts with its orbital motion. According to the researchers, this strong coupling enables them to control the particle's spin with an electric field.

The researchers have also measured how strongly a hole's spin-orbit coupling could be engineered with an electric field. They claim to have shown that an external electric field could tune the strength of the coupling.

More recently, the researchers measured how strongly a hole's spin interacts with a magnetic field. In these experiments, they applied constant magnetic fields of different strengths parallel to the diamond surface at temperatures below 4 Kelvin. They also simultaneously applied a steadily varying perpendicular field. By monitoring how the electrical resistance of the diamond changed, they said they were able to determine the g-factor. They believe this quantity could aid control spin in future devices using a magnetic field.

"The coupling strength of carrier spins to electric and magnetic fields lies at the heart of spintronics," Golrokh Akhgar, a physicist at La Trobe University, explained. "We now have the two crucial parameters for the manipulation of spins in the conductive surface layer of diamond by either electric or magnetic fields."

As diamond is transparent, the researchers said it could be incorporated into optical devices that operate with visible or ultraviolet light.

Nitrogen-vacancy diamonds, which contain nitrogen atoms paired with missing carbon atoms in its crystal structure, apparently showed promise as a quantum bit, or qubit.

The hope is that the team will be able to manipulate spin and use it as a qubit, which may lead to more devices with untapped potential in the future.

Bethan Grylls

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