New Discovery Can Give Faster Spintronic Elements
Uppsala physicists have been able to show that there is a new form of magnetic torque which may make spintronic elements even faster than they are today. The research has been published in Nature Communications.
Within spintronics, the electron’s magnetic properties, their spin, are used for various types of storage and processing of data. In the future the spin momentum of one single atom in a material is expected to become the smallest magnetic carrier of data. But a new type of technology is needed to be able to influence the magnetic moments on individual atoms even faster than today and at lower energy costs.
A promising way to accomplish this change in a material, a so called switch, is to use the spin-orbit torque that originate from the spin-orbit coupling in the material. The spin-orbit torque occurs when an electric current is sent through the material, through the so called Rashba-Edelstein effect, of which the Russian physicists Rashba and Edelstein laid the foundation for in the 60s and 80s. But a lot about how this works is still unknown.
The Uppsala researchers Leandro Salemi, Marco Berritta, Ashis Nandy and Peter Oppeneer have now shown that there are new forms of the Rashba-Edelstein effect in topological antiferromagnets, which have special symmetry properties. These topological antiferromagnets possess spatial mirror symmetry together with time reversal symmetry, which makes it possible to change the atom’s magnetic moment to the opposite direction, that is, to create a switch of the atomic moments. Through accurate relativistic quantum mechanical calculations, the Uppsala physicists could show that electric currents lead to a large magnetic orbital momentum on the atoms, i.e. a large total magnetic orbital momentum that arises as the electrons move around the atomic nucleus.
The image shows a model of mirror symmetry together with time reversal symmetry in an antiferromagnet, for example CuMnAs or Mn2Au. The current J leads to an induced magnetic orbital momentum on the atoms A and B which exerts a torque tL that makes the atom’s spin momentum (red vector) switch. Image: Leandro Salemi.
Calculations on the antiferromagnets CuMnAs and Mn2Au showed that the orbital momentum created under the influence of an external electric field is almost 45 times higher than the spin momentum and may thereby lead to a larger spin-orbit momentum. They could also show that the induced orbital momentum and the spin-orbit momentum can be driven by electric fields of very high frequencies, which opens up new perspectives for super-fast spintronics in the order of 1015 Hz in the future.
“I was very surprised when I received an email from Professor Rashba, who has passed 90 years, and who especially praised our research progress in quantum spintronics”, says Leandro Salemi, PhD at the Department of Physics and Astronomy.
Article reference
Leandro Salemi, Marco Berritta, Ashis Nandy & Peter Oppeneer (2019), Orbitally dominated Rashba-Edelstein effect in noncentrosymmetric antiferromagnets, Nature Communications 2019, 10, 5381, DOI: 10.1038, https://doi.org/10.1038/s41467-019-13367-z
Contact
Leandro Salemi, tel. 0723 654186, leandro.salemi@physics.uu.se
Peter Oppeneer, tel. 0709 604016, peter.oppeneer@physics.uu.se
Translation: Johan Wall