Stochastic switching time constant and instability in nanomagnets

The Arrhenius law governs thermally-activated phenomena with a pre-exponential factor, the attempt time τ0, which defines the time constant of stochastic process. In nanomagnets, accessing τ0 is a formidable task due to the temperature-dependent magnetic properties that preclude the use of a standard Arrhenius plot and lead to the questionable assumption that τ0 = 1 ns for several decades. This is an untenable situation considering τ0’s critical role in the performance of stochastic magnetic tunnel junctions (s-MTJs), particularly in the context of unconventional computing. Here we present a systematic measurement of τ0 and reveal the governing physics. By analyzing the random telegraph noise as a function of applied magnetic fields along the hard axis, we derive a magnetic version of the Arrhenius plot, arriving at τ0 = 3.7–12 ns depending on the perpendicular magnetic anisotropy. Furthermore, we reveal that the Suhl instability significantly increases τ0 by the emission of spin waves. The results renew the understanding of stochastic dynamics in nanomagnets, offering a route to design high-performance s-MTJs. The Arrhenius law’s pre-exponential factor, τ0, is crucial for understanding stochastic processes in nanomagnets, yet its accurate measurement has long been elusive. Here, the authors systematically measure τ0 using a magnetic Arrhenius plot, revealing values of 3.7–12 ns depending on the perpendicular magnetic anisotropy, and uncovering significant increases in τ0 driven by spin-wave emission, thus advancing the design of high-performance stochastic magnetic tunnel junctions.