Prospect of Antiferromagnetic Spintronics Challenged
Spintronic devices based on ferromagnetic (FM) materials, from high-density magnetic recording to magnetic random-access memories (MRAMs), have been the leading technologies for decades. But FM materials generate stray field, and are susceptible to magnetic field. For the past 5 years, theorists and experimentalists have suggested antiferromagnetic spintronics may hold the future, where antiferromagnetic (AF) materials with zero net magnetization are used, thus immune to magnetic field and generating no stray field, with the added advantage of terahertz frequencies for ultrafast dynamics. But switching of AF material is a formidable obstacle. Recently, there have been numerous reports of electrical switching of AF Néel vector via spin-orbit torque (SOT), attracting worldwide attention. By applying a write current in the AF layer or the normal metal (NM)/AF bilayer, in a patterned multiterminal structure, the measured resistance shows recurring signals due to supposedly electrical switching of the AF Néel vector. However, the researchers including those at the Department of Physics (Professor Ssu-Yen Huang) of the National Taiwan University and the Institute of Physics (Dr. Danru Qu) of Academia Sinica demonstrate that similar signals can be observed in such patterned structures, with and without the AFM layer. This widely held switching signal may not be conclusive evidence of SOT switching of AFM but the thermal artifacts of patterned metal structure on substrate. We show that under a large writing current density beyond the Ohmic regime, the multiterminal devices can generate unintended anisotropic thermal gradients and voltages. As a consequence, the strength of the signal is greatly affected by the thermal conductivity of the substrates. Our results seriously question the validity of SOT switching of AF Néel vector and indeed the prospect of AF spintronics. We indicate AF switching requires unequivocal detection of the AF Néel vector before and after the SOT switching. This work is published in Physical Review Letter (Phys. Rev. Lett. 123, 227203 (2019)) and is Featured in Physics and highlighted as an Editor’s Suggestion.
1. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.227203
2. https://physics.aps.org/articles/v12/134
WebSite: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.227203