New Hybrid Material for Spin Transistors of the Future

Spin-based transistors could replace conventional transistors in the future. Spin transistors require significantly less energy, but industrial conversion has so far failed due to the lack of a suitable material. The young scientist Zeila Zanolli has now found a novel combination of graphite and barium manganese oxide, which meets the contradictory requirements. The hybrid material allows both precise spin alignment and good spin transport, as demonstrated by simulations on supercomputers at the Jülich Supercomputing Center (JSC).

Structure of the hybrid material made of graphene (top, bottom) and Bariummanganoxid (center) Copyright: Zanolli, Sci. Rep. 6, 31346, 2016 (CC BY 4.0)

Transistors are probably the most important basic building blocks of modern memory sticks and processors.Up to several billions of them are on current computer chips. The current types of transis- tors use only the electric charge of the electron to switch from one state to the other. The switching processes in a spin-based transistor, on the other hand, are based on changes in the electron spin, like all applications in the field of spintronics.The energy to be applied for this purpose would be an order of magnitude lower than that required for switching a conventional transistor, which would result in immense energy savings.

However, the implementation of spin transistors is made more difficult by contrasting material requirements.Traditional semiconductors, such as those currently used in chip manufacturing, offer a strong spin-orbit coupling: the electron spin can be aligned well with an external field. However, the spin polarization achieved in this way is only extremely short distances and can not be maintained sufficiently long to manipulate the spins subsequently. In novel carbon-based semiconductors, such as carbon nanotubes or graphene, the spin polarization is retained over long distances, but can not be controlled externally.

But the advantages of both material classes are complementary when combining graphs with a magnetic semiconductor. The young scientist Zeila Zanolli was able to demonstrate the remarkable quality of a Marie Curie Fellowship at Forschungszentrum Jülich at the Peter Grünberg Institute (PGI-1). The Jülich supercomputers JUQUEEN and JURECA, which are among the fastest computers in Europe, were used for the computationally intensive analysis. Zanolli, who is now headed by the DFG research group Nanospintronics at RWTH Aachen University, was able to demonstrate with the help of computer simulations: the new material combination “inherits” the great spin propagation length of the graphene. At the same time, the interaction is so strong that the polarization of the electron spin is transferred to the graph by the manganese atoms.