A research team led by Johannes Gutenberg-University Mainz, which also included Forschungszentrum Jülich and JARA, The University of Tokyo, HZB and Institut Polytechnique de Paris, has demonstrated a purely orbitronic device concept in which orbital currents are used directly, without conversion into spin currents, to generate exceptionally large magnetoresistance signals in antiferromagnetic heterostructures.
Building on recent predictions that orbital current effects can exceed spin-current effects by orders of magnitude, the team shows that these giant orbital currents can be harnessed in practice by replacing conventional spin-dominated magnets with magnets dominated by orbital angular momentum (OAM). This work, led by Dr. Christin Schmitt in the group of Professor Mathias Kläui at Johannes Gutenberg University Mainz (JGU), was carried out with more than twenty international collaborators.
The researchers are said to be the first to directly utilize orbital currents without the need for conversion of the orbital current into a spin current. Orbitronics is based on orbital moments - the quantum-mechanical “vortices” of electrons around atomic nuclei - and orbital currents, the transport of these circulations through an electrical conductor. Orbital currents offer a significant advantage over spin currents because the measurable signals are orders of magnitude stronger, which means that using orbital currents to write or read information in magnetic memories can enable substantially more efficient switching processes and extremely low energy consumption device concepts. “We have thus realized the first purely orbitronic device approach,” said Schmitt, emphasizing that “for the first time, we have been able to directly couple mobile orbital moments with localized orbital moments in a magnet. In doing so, we have achieved a milestone in orbitronics and laid the foundation for significantly more energy-efficient data storage. In this way, we obtain signals that are two orders of magnitude stronger than those in conventional spintronic devices.”
To realize and probe this orbitronic mechanism, the team used cobalt oxide (CoO) as an insulating antiferromagnet with a copper layer that reacts at the surface to form copper oxide (Cu). In this CoO/Cu heterostructure, orbital currents are generated at the copper–copper oxide surface and propagate toward the cobalt oxide, where they interact with localized orbital moments in the antiferromagnet. By choosing a magnet dominated by orbital angular momentum, the researchers achieve direct coupling between the mobile orbital moments in copper and the static orbital moments in cobalt. This coupling is essential for information readout: depending on how the orbital moments in copper and cobalt are aligned with respect to each other, the system represents a logical “0” or “1”. “The coupling became possible because we used a magnet dominated by orbital angular momentum, whereas previous studies had always relied on spin-dominated magnets,” Schmitt explained.
The authors report a 70-fold enhancement in orbital Hall magnetoresistance in CoO/Cu compared with spin Hall magnetoresistance in a reference CoO/Pt system, where information can be stored and read out using pure spin currents. In the spin-based CoO/Pt stack, spin currents generated in platinum interact with the antiferromagnetic CoO and give rise to a magnetoresistance signal. In the orbitronic CoO/Cu stack, the dynamic OAM from surface-oxidized Cu couples to the static OAM in CoO, producing an orbital Hall magnetoresistance signal that is 70 times larger than the spin Hall magnetoresistance in CoO/Pt and, overall, two orders of magnitude stronger than signals in conventional spintronic devices. “With the orbitronic system, we were able to increase the resulting signal by two orders of magnitude compared with the signal generated by pure spin currents,” Schmitt summarized.
Dr. Sachin Krishnia, a senior member of the research team, emphasized that the effect is not only stronger but also fundamentally different in physical terms: “Beyond the magnitude of the signal, what is crucial is that the orbital current interacts with the cobalt oxide in a completely different way. It does not simply mimic a spin current; rather, it appears to activate hidden properties of the antiferromagnet. This makes orbital magnetism an active degree of freedom for future devices.” This makes clear that orbital Hall magnetoresistance is not just a scaled-up analogue of spin Hall magnetoresistance; instead, it probes and uses the orbital angular momentum texture of the antiferromagnet itself, opening a path to device concepts that cannot be accessed with spin currents alone.
Orbitronics is presented as a promising technology for future memory and computing devices because it could enable large-scale storage media with extremely low energy consumption. Today, spin currents are used to control the magnetic state of ferromagnets in technologies such as spin-orbit torque magnetic random-access memory, but material choices are constrained by the need for strong spin–orbit coupling to generate sufficiently large spin currents. In contrast, the orbitronic approach couples orbital currents directly to orbital magnetization in CoO/Cu heterostructures, harnessing giant orbital currents in OAM-dominated materials and bypassing some of the limitations associated with spin–orbit coupling. Schmitt sees considerable potential for future applications: “Antiferromagnetic materials with strong orbital properties therefore constitute a good platform for future orbital devices. By enabling more energy-efficient memory and computing technologies, they could help address challenges related to resources, energy consumption, and climate change.”
The head of the research team, Mathias Kläui, stressed that this breakthrough relies on long-term international collaboration across materials growth, device fabrication and theory. “For more than ten years, we have been working with colleagues in Japan as part of projects funded by the German Academic Exchange Service and the Japan Society for the Promotion of Science. This enables JGU students to produce there the required high-quality materials together with colleagues on site. And the theoretical work was carried out within the framework of German and EU-funded projects. Such international collaborations make possible exciting new research that we could never have realized on our own.” By combining high-quality CoO/Cu heterostructures from the University of Tokyo with expertise from Mainz, Jülich, JARA, HZB and Institut Polytechnique de Paris, the team has turned the conceptual advantage of giant orbital currents into a concrete, device-relevant orbitronic magnetoresistance effect.