Simplified schematic of the magnetic graphene-based spintronic device, showing electrical and thermal generation of spin currents in the bilayer graphene/CrSBr heterostructure. Magnetic cobalt electrodes are used to determine the degree of proximity-induced spin polarization in the bilayer graphene, where the magnetization of the outer-most layer of CrSBr (MCSB) allows for higher conductivity of the spin-up electrons (red arrows). Image: Talieh Ghiasi, University of Groningen.
Simplified schematic of the magnetic graphene-based spintronic device, showing electrical and thermal generation of spin currents in the bilayer graphene/CrSBr heterostructure. Magnetic cobalt electrodes are used to determine the degree of proximity-induced spin polarization in the bilayer graphene, where the magnetization of the outer-most layer of CrSBr (MCSB) allows for higher conductivity of the spin-up electrons (red arrows). Image: Talieh Ghiasi, University of Groningen.

Experiments by physicists at the University of Groningen in the Netherlands and Colombia University suggest that magnetic graphene could be an ideal material for producing ultra-compact spintronic devices. This follows their discovery that magnetic graphene can efficiently convert charge to spin current and transfer this strong spin-polarization over long distances, which they report in a paper in Nature Nanotechnology.

Spintronic devices are promising high-speed and energy-saving alternatives for current electronics. These devices use the magnetic moment of electrons, known as spin, which can be 'up' or 'down', to transfer and store information. The ongoing scaling down of memory technology requires ever smaller spintronic devices, and thus researchers have been looking for atomically thin materials that can actively generate large spin signals and transfer the spin information over micrometer-long distances.

For over a decade, graphene has been the most favourable 2D material for the transport of spin information. However, graphene cannot generate spin current by itself unless its properties are appropriately modified. One way to achieve this is to make it act as a magnetic material. This magnetism would favour the passage of one type of spin and thus create an imbalance in the number of electrons with spin-up versus spin-down, resulting in a highly spin-polarized current.

This idea has now been experimentally confirmed by scientists in the Physics of Nanodevices group at the University of Groningen, led by Bart van Wees. When the physicists brought graphene in close proximity to a 2D layered antiferromagnet, CrSBr, they were able to directly measure a large spin-polarization of current, generated by the magnetic graphene.

In conventional graphene-based spintronic devices, ferromagnetic (cobalt) electrodes are used for injecting and detecting the spin signal into graphene. In contrast, in circuits built from magnetic graphene, the injection, transport and detection of the spins can all be done by the graphene itself.

"We detect an exceptionally large spin-polarization of conductivity of 14% in the magnetic graphene that is also expected to be efficiently tuneable by a transverse electric field," says Talieh Ghiasi, first author of the paper, This, together with the outstanding charge and spin transport properties of graphene, allows for the realization of all-graphene 2D spin-logic circuitries where the magnetic graphene alone can inject, transport and detect spin information.

Moreover, the unavoidable heat dissipation that happens in any electronic circuitry becomes an advantage in these spintronic devices. "We observe that the temperature gradient in the magnetic graphene due to the Joule heating is converted to spin current," Ghiasi explains. "This happens by the spin-dependent Seebeck effect that is also observed in graphene for the first time in our experiments." The efficient electrical and thermal generation of spin currents by magnetic graphene promises substantial advances for both 2D spintronic and spin-caloritronic technologies.

In addition, because the spin transport in graphene is highly sensitive to the magnetic behaviour of the outer-most layer of the neighbouring antiferromagnet, these spin transport measurements could offer a way to probe the magnetization of a single atomic layer. Thus, these magnetic graphene-based devices could not only address the most technologically relevant aspects of magnetism in graphene for 2D memory and sensory systems, but could also provide further insight into the physics of magnetism.

This story is adapted from material from the University of Groningen, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.