Stochastic Magnetic Tunnel Junctions for Probabilistic Computing and Solving Combinatorial Optimization Problems

Professor Andrew Kent at ECE spring 2026 colloquium

Magnetic tunnel junctions (MTJs) are widely used as nonvolatile memory elements, but they can also serve as controllable, high-rate sources of random bits. In this talk, I will describe experimental studies of perpendicularly magnetized MTJs that are magnetically stable at room temperature. Instead of relying on spontaneous thermal magnetization fluctuations (superparamagnetism), stochastic behavior is generated on demand by actuating the device with nanosecond electrical pulses in the ballistic spin-transfer regime. This approach enables precise control of the switching probability. I will present measurements showing high-rate (up to 100 MHz/MTJ), reproducible generation of random bit streams and random telegraph noise. By interfacing individual pMTJs with custom electronics and a field-programmable gate array (FPGA), we generate truly random numbers that pass the full NIST statistical test suite with no post-processing. I will also show how such actuated stochastic MTJs (A-sMTJs) can be electrically connected in simple circuits to generate tunable, circuit-mediated interactions that map onto effective Ising couplings. Finally, I will discuss the potential of stochastic MTJs or physics-inspired computing systems, including their use for solving combinatorial optimization problems.