The study demonstrates the generation of orbital current through magnetization dynamics

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

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

Researchers at Keio University and Johannes Gutenberg University report the successful generation of an orbital current from magnetization dynamics, a phenomenon called orbital pumping. Their paper, published in Nature Electronicsdescribes a promising approach that could allow engineers to develop new technologies exploiting the orbital angular momentum of electrons.

“Our work was inspired by ongoing research in spintronics and orbitronics, the orbital analogs of spintronics,” Kazuya Ando, ​​Associate Professor at Keio University, told Phys.org.

“Spintronics has advanced through the exploration of the physics of spin current, the flow of spin angular momentum. Recent studies have highlighted the crucial role of orbital current, the spin current’s counterpart, in solid-state devices. However, the generation of orbital currents has remained an important challenge”.

The latest study by Ando and his colleagues takes inspiration from eddy pumping, a well-established phenomenon that allows engineers to generate eddy currents. The main objective 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 understanding of orbitronics and opens new avenues for research and technological applications,” Ando said.

Orbital pumping essentially involves the generation of an orbital current through magnetization dynamics (ie, the density of magnetic dipole moments induced in magnetic materials when they are placed near a magnet). To perform their experiments, Ando and his colleagues specifically used a bilayer structure made of nickel and titanium.

“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 discovered this electric orbital current using the inverse orbital Hall effect, a phenomenon that converts an 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. The techniques they used thus eventually proved effective in generating an orbital current in an experimental setting.

“In the development of spin current-based spintronics, spin pumping has played a crucial role, revealing a variety 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 basis 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 aimed at generating orbital currents through magnetization. These works may 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 to develop devices that use both spin and orbital angular momentum of electrons. Through these efforts, we hope to advance the fields of spintronics and orbitronics, paving the way for new electronic technologies.”

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