Correlated fluctuations in spin orbit torque-coupled perpendicular nanomagnets

Abstract

Low barrier nanomagnets have attracted a lot of research interest for their use as sources of high quality true random number generation. More recently, low barrier nanomagnets with tunable output have been shown to be a natural hardware platform for unconventional computing paradigms such as probabilistic spin logic. Efficient generation and tunability of high quality random bits is critical for these novel applications. However, current spintronic random number generators are based on superparamagnetic tunnel junctions (SMTJs) with tunability obtained through spin transfer torque (STT), which unavoidably leads to challenges in designing concatenated networks using these two terminal devices. The more recent development of utilizing spin orbit torque (SOT) allows for a three terminal device design, but can only tune in-plane magnetization freely, which is not very energy efficient due to the needs of overcoming a large demagnetization field. In this work, we experimentally demonstrate for the first time, a stochastic device with perpendicular magnetic anisotropy (PMA) that is completely tunable by SOT without the aid of any external magnetic field. Our measurements lead us to hypothesize that a tilted anisotropy might be responsible for the observed tunability. We carry out stochastic Landau-Lifshitz-Gilbert (sLLG) simulations to confirm our experimental observation. Finally, we build an electrically coupled network of two such stochastic nanomagnet based devices and demonstrate that finite correlation or anti-correlation can be established between their output fluctuations by a weak interconnection, despite having a large difference in their natural fluctuation time scale. Simulations based on a newly developed dynamical model for autonomous circuits composed of low barrier nanomagnets show close agreement with the experimental results.

References in corpus (15)

• Spin torque switching with the giant spin Hall effect of tantalum
• Magnetic switching by spin torque from the spin Hall effect
• Switching of perpendicular magnetization by spin-orbit torques in the absence of external magnetic fields
• Magnetization switching by spin-orbit torque in an antiferromagnet/ferromagnet bilayer system
• Quantitative characterization of the spin orbit torque using harmonic Hall voltage measurements
• Electric field control of deterministic current-induced magnetization switching in a hybrid ferromagnetic/ferroelectric structure
• Stochastic p-bits for Invertible Logic
• Switching of Perpendicularly Polarized Nanomagnets with Spin Orbit Torque without an External Magnetic Field by Engineering a Tilted Anisotropy
• Intrinsic optimization using stochastic nanomagnets
• Tuning a binary ferromagnet into a multi-state synapse with spin-orbit torque induced plasticity
• Low-Energy Truly Random Number Generation with Superparamagnetic Tunnel Junctions for Unconventional Computing
• Low Barrier Nanomagnets as p-bits for Spin Logic
• Spin Logic Devices via Electric Field Controlled Magnetization Reversal by Spin-Orbit Torque
• Implementing Bayesian Networks with Embedded Stochastic MRAM
• Voltage-driven Building Block for Hardware Belief Networks

Cited by in corpus (10)

• Roadmap of spin-orbit torques
• A full-stack view of probabilistic computing with p-bits: devices, architectures and algorithms
• Experimental demonstration of an integrated on-chip p-bit core utilizing stochastic Magnetic Tunnel Junctions and 2D-MoS2 FETs
• Hardware Design for Autonomous Bayesian Networks
• Mutual control of stochastic switching for two electrically coupled superparamagnetic tunnel junctions
• Spin torque gate magnetic field sensor
• A vector magnetometer based on a single spin-orbit torque anomalous Hall device
• Metrics for spin-based computing
• Spin orbit torque controlled stochastic oscillators with synchronization and frequency tunability
• In-plane dominant anisotropy stochastic magnetic tunnel junction for probabilistic computing: A Fokker-Planck study