Solving Combinatorial Optimization Problems Stochastic Magnetic Tunnel Junctions

---

Can stochastic magnetic tunnel junction arrays solve complex optimization

problems better than existing methods? The first part of this talk addresses this

question by presenting the Sherrington–Kirkpatrick (SK) spin-glass model, a

difficult problem with a known solution in the thermodynamic limit.

Remarkably, we show by numerical modeling that coupled macrospins

emulating the SK model and evolving according to Landau-Lifshitz Gilbert

dynamics can get closer to the true ground state energy than state-of-the-art

numerical methods [1].

The second part of my talk will focus on stochastic magnetic tunnel junctions based on perpendicular magnetic

tunnel junctions. In contrast to superparamagnetic MTJs, we experiment with magnetically stable perpendicularly

magnetized MTJs (pMTJs) and actuate them with nanosecond pulses to make them behave stochastically. We

denote this a stochastic magnetic actuated random transducer (SMART) pMTJ device because a pulse generates

a random bit stream on-demand, much like a coin flip [2]. SMART-pMTJs produce truly random bit streams at

very high rates (>100MHz) [3], while being more robust to environmental changes, such as their operating

temperature and device-to-device variations, compared to other stochastic nanomagnetic devices [4,5]. By

interfacing a SMART-pMTJ to an FPGA, we have generated over 1 trillion bits at rates greater than 100 MHz

that pass multiple statistical tests for true randomness, including all the NIST tests for random number generators

with only one XOR operation [6]. Finally, I will discuss opportunities to advance the science and applications of

stochastic MTJs toward creating better sources of random numbers and addressing complex optimization

problems.

[1] Dairong Chen, Andrew D. Kent, Dries Sels and Flaviano Morone, “Solving combinatorial optimization problems through stochastic Landau-

Lifshitz-Gilbert dynamical systems,” arXiv:2407.00530

[2] L. Rehm, C. Capriata, S. Misra, J. Smith, M. Pinarbasi, B. Malm, and A. D., Kent, “Stochastic magnetic actuated random transducer devices based

on perpendicular magnetic tunnel junctions,” Phys. Rev. Appl. 19, 024035 (2023)

[3] Ahmed Sidi El Valli, Michael Tsao, J. Darby Smith, Shashank Misra, and Andrew D. Kent. “High-Speed Tunable Generation of Random Number

Distributions Using Actuated Perpendicular Magnetic Tunnel Junctions,” arXiv:2501.06318

[4] L. Rehm, M. G. Morshed, S. Misra, A. Shukla, S. Rakheja, M. Pinarbasi, A. W. Ghosh, and A. D. Kent, “Temperature-resilient true random number

generation with stochastic actuated magnetic tunnel junction devices,” Appl. Phys. Lett. 124, 052401 (2024)

[5] Md Golam Morshed, Laura Rehm, Ankit Shukla, Yunkun Xie, Samiran Ganguly, Shaloo Rakheja, Andrew D. Kent, Avik W. Ghosh, "Reduced

sensitivity to process, voltage and temperature variations in activated perpendicular magnetic tunnel junctions based stochastic devices,"

arXiv:2310.18781

[5] A. Dubovskiy, T. Criss, A. Sidi El Valli, L. Rehm, A. D. Kent, A. Haas, "One Trillion True Random Bits Generated With a Field-Programmable Gate

Array Actuated Magnetic Tunnel Junction," IEEE Magnetics Letters 15 (2024)

---

---

---

---

2024_MAT-PULSE_Seminar__Andrew_Kent_-_June__13th_

464.01 KiB

---