Electrical Control of Antiferromagnetic Order for High-Performance and Energy-Efficient Computing

Pedram Khalili, Northwestern University

July 10, 2020

Antiferromagnets are magnetically ordered materials without a macroscopic magnetization. As a result, they are of interest in the development of memory devices where data cannot be erased by external magnetic fields. However, the absence of a macroscopic moment also makes it difficult to electrically control their magnetic order (Néel vector). Here we show that pillars of antiferromagnetic PtMn, which are grown on heavy metal layers of Pt and Ta, can be reversibly switched between different magnetic states by electric currents [1] (See Fig. 1). The devices are based on materials that are typically used in the magnetic memory industry, and we observe switching with low current densities.  Furthermore, by varying the amplitude of the writing current, multi-level memory characteristics can be achieved. Micromagnetic simulations suggest that the different magnetic states may consist of domains separated by domain walls with vortex and anti-vortex textures that move in response to current, modifying the average Néel vector. 

As a strategy to further improve the energy efficiency of antiferromagnetic memory, we then examine the voltage-controlled magnetic anisotropy effect in antiferromagnetic materials interfaced with oxides. We propose a method for switching the Néel vector of an antiferromagnetic thin film, by the application of an ultrashort electric field pulse [2]. The electric field induces a resonant reorientation of the antiferromagnetic order parameter, due to the voltage-induced modification of the magnetic anisotropy. Importantly, the electric field required to induce this reversal is as small as ~ 100 mV/nm, comparable to fields used for switching of ferromagnetic tunnel junctions in earlier works. This electric field is determined by the anisotropy of the antiferromagnet, while the much larger exchange field determines the frequency of the resulting dynamics (and hence the switching time, which is in the picoseconds range). The current- and voltage-induced switching of the Néel vector presented in this work opens a new route towards energy-efficient and ultrafast memories and computing devices based on antiferromagnets.

[1] J. Shi, V. Lopez-Dominguez, F. Garesci, C. Wang, H. Almasi, M. Grayson, G. Finocchio, P. Khalili Amiri, Electrical manipulation of the magnetic order in antiferromagnetic PtMn pillars, Nature Electronics 3, 92 (2020).
[2] V. Lopez-Dominguez, H. Almasi, P. Khalili Amiri, Picosecond electric-field-induced switching of antiferromagnets, Phys. Rev. Applied 11, 024019 (2019).