The study demonstrates the generation of orbital current through magnetization dynamics

Electrons inherently carry both spin and orbital angular momentum (ie, properties that help understand the rotational motions and behavior of particles). While some physicists and engineers have attempted to use the spin angular momentum of electrons to develop new technologies known as spintronics, the orbital momentum of these particles has rarely been considered.

Currently, the generation of an orbital current (ie, the flow of orbital angular momentum) remains much more challenging than the generation of a spin current. However, approaches to successfully exploit the orbital angular momentum of electrons could open the possibility for the development of a new class of devices called orbitronics.

Researchers from Keio University and Johannes Gutenberg University report the successful generation of orbital current from magnetization dynamics, a phenomenon called orbital pumping. Their work, published in Natural electronicsoutlines a promising approach that could allow engineers to develop new technologies using the orbital angular momentum of electrons.

“Our work was inspired by ongoing research on spintronics and orbitronics, the orbital analog of spintronics,” Kazuya Ando, ​​an associate professor at Keio University, told Phys.org.

“Spintronics has advanced by investigating the physics of spin current, the flow of spin angular momentum. Recent studies have highlighted the essential role of orbital current, the spin current’s counterpart, in solid-state devices. However, the generation of orbital currents has remained a significant challenge.”

A recent study by Ando and his colleagues draws inspiration from spin pumping, a well-established phenomenon that allows engineers to generate spin currents. The main goal of their study was to realize the orbital counterpart of this phenomenon, called orbital pumping.

“We believe the demonstration of orbital pumping expands the fundamental knowledge of orbitronics and opens new avenues for research and technological applications,” Ando said.

Orbital pumping essentially means the generation of an orbital current through magnetization dynamics (ie, the density of magnetic dipole moments induced in magnetic materials when placed near a magnet). Specifically, Ando and his colleagues used a two-layer structure made of nickel and titanium to perform their experiments.

“By applying a radio-frequency magnetic field to the structure, we excited the magnetization dynamics in the nickel layer, which in turn generated an orbital current in the titanium layer through orbital pumping,” Ando explained. “We detected this orbital current electrically using the inverse orbital Hall effect, a phenomenon that converts the orbital current into a charge current.”

By applying a magnetic field to their nickel and titanium structure, the researchers were able to successfully demonstrate orbital pumping. Thus, the techniques they used eventually proved effective in generating orbital current in an experimental environment.

“In the development of spin current-based spintronics, spin pumping has played a key role, revealing a number of phenomena and functions arising from spin currents,” Ando said. “Similarly, our discovery of orbital pumping, the orbital counterpart of spin pumping, is expected to serve as a fundamental foundation for new electronic technologies and physics based on orbital currents.”

The promising results achieved by Ando and his colleagues may soon pave the way for new studies focused on the generation of orbital currents using magnetization. These works could eventually lead to the introduction of orbitronic devices, a class of electronics that has so far been largely overlooked.

“Our future research will focus on further understanding the fundamental properties of orbital currents and their interactions with magnetization dynamics,” Ando added.

“We also aim to elucidate the combined effects of spin currents and orbital currents in order to develop devices that utilize both the spin and orbital angular momentum of electrons. We hope that this effort will advance the field of spintronics and orbitronics and pave the way for new electronic technologies.”

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