Shaloo Rakheja - An engineer’s perspective on antiferromagnetic spintronics

Antiferromagnets (AFM) materials have ordered spin moments that alternate between individual atomic sites, which gives them a vanishing macroscopic magnetic signature and picosecond intrinsic timescale. In his 1970 Nobel Lecture, Louis Néel claimed that antiferromagnets are “extremely interesting from theoretical standpoint, but do not seem to have any applications.” Traditionally, AFM materials have played a secondary role to ferromagnets, which are used as active elements in commercial spintronic devices like magnetic sensors and non-volatile magnetic memory. However, it was recently suggested that spin transfer torque could in principle be used to manipulate the magnetic order in AFMs, leading to either stable AFM order precessions for their use as high-frequency oscillators, or switching of the AFM order for their use as magnetic memories.

My presentation will focus on recent theoretical and experimental developments in the field of spintronic devices using antiferromagnets as their active elements. I will specifically talk about two unique AFM materials, Cr2O3, a single-phase magnetoelectric material that can be manipulated solely with electric fields and the Weyl semi-metal Mn3Sn in which spin torque can induce chiral spin rotations. Cr2O3-based ferromagnet-free random access memory has been experimentally demonstrated, while in the case of Mn3Sn, spin torque driven dynamics were found to induce chiral oscillations, from the megahertz to the terahertz frequency range. These materials can overcome the central challenge of manipulating and reading the AFM’s order parameter via microelectronics compatible circuitry, thus allowing us to develop antiferromagnetic spintronics along a similar route as ferromagnetic spintronics.

I will conclude my talk by summarizing the limits, challenges, and opportunities of AFM spintronics for future technologies such as high-density, secure nonvolatile memory, compact narrowband terahertz sources, and spike generators.