Dynamical stability by spin transfer in nearly isotropic magnets

Abstract

Spin transfer torques (STTs) control magnetization by electric currents, enabling a range of nano-scale spintronic applications. They can destabilize the equilibrium magnetization state by counteracting magnetic relaxation. Here we maximize the STT effect through a dedicated growth-annealing protocol for CoFeB thin films, such that magnetic anisotropies originating from the interface and shape almost cancel each other. The nearly isotropic magnets enable low-current dynamical stabilization of the magnetization in the direction opposite to an applied magnetic field, thereby realizing a spintronic analogue of the Kapitza pendulum. In an intermediate current regime, the STT drives large magnetization vector fluctuations that cover the entire Bloch sphere. The continuous variable associated with the stochastic magnetization direction may serve as a resource for probabilistic computing and neuromorphic hardware. Our results establish isotropic magnets as a platform to study as-yet-uncharted, far-from-equilibrium spin dynamics including anti-magnonics, with promising implications for unconventional computing paradigms.