A Study of Spin-Orbit Torques and Field-Free Deterministic Switching of Perpendicular Magnetization

Speaker: Seyed Armin Razavi
Affiliation: Ph.D. Candidate

Via Zoom: https://ucla.zoom.us/j/92582427335

Abstract:   Spintronic devices provide an energy-efficient platform for implementing non-volatile memory and logic. In spintronic memory devices, the information is stored in the magnetization state of the free magnetic layer, and current, voltage or strain-induced mechanisms are used for switching the magnetization. Among the operation methods, current-induced spin-orbit torque (SOT) is a promising mechanism for magnetization switching with faster dynamics, higher endurance, and potentially higher energy efficiency compared to the conventional spin-transfer torque. For magnetic memory applications, perpendicular magnetic anisotropy is desirable since it enables high memory densities. However, for deterministic SOT switching of a perpendicular magnet, an external in-plane magnetic field collinear with the current is required, which hampers the applicability of SOT switching.

We present two main approaches for realizing deterministic field-free SOT switching for practical uses. First, we show that the external in-plane field can be replaced by a built-in exchange bias field using antiferromagnetic materials. We also show that certain antiferromagnets can create the SOTs themselves, serving as the layer providing both the exchange bias and SOTs. As the second approach, we use the concept of structural asymmetry reported previously, and modify the conventional SOT heterostructure by inserting a slightly asymmetric light-metal at the heavy-metal/ferromagnet interface. The broken structural symmetry enables the creation of current-induced out-of-plane effective magnetic fields, which break the symmetry between the up and down states for each current polarity and allow for deterministic SOT switching at zero external magnetic field. We also apply the asymmetry concept to a second material system with a minimal structural asymmetry, resulting in an enhanced magnetic uniformity across large wafer areas. We show that the latter approach for field-free SOT switching has all the characteristics of a practical solution that could be used in applications.

Biography: Seyed Armin Razavi is a Ph.D. candidate at the Device Research Laboratory (DRL) in the Electrical & Computer Engineering Department at UCLA. He received the B.S. degree in Electrical Engineering from Sharif University of Technology, Tehran, Iran, in 2014, and the M.S. degree in Electrical Engineering from UCLA in 2017. He has broad research interests in spintronics, magnetism, condensed matter physics and quantum devices. He was a recipient of the UCLA Electrical Engineering Departmental Fellowship in 2014.

For more information, contact Prof. Kang L. Wang (wang@ee.ucla.edu)

Date/Time:
Date(s) - Oct 01, 2020
2:00 pm - 4:00 pm

Location:
Via Zoom Only
No location, Los Angeles
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