Dynamical stability by spin transfer in nearly isotropic magnets

TL;DR

This paper demonstrates how nearly isotropic CoFeB thin films, optimized through growth-annealing, enable low-current spin transfer torque effects that stabilize and induce complex dynamics in magnetisation, opening new avenues for spintronic applications and unconventional computing.

Contribution

It introduces a method to create nearly isotropic magnets with maximized spin transfer torques, enabling novel dynamical control of magnetisation.

Findings

Low-current dynamical stabilization of magnetisation opposite to magnetic field.

Large magnetisation fluctuations covering the entire Bloch sphere.

Potential for probabilistic computing and neuromorphic hardware.

Abstract

Spin transfer torques (STTs) control magnetisation by electric currents, enabling a range of nano-scale spintronic applications. They can destabilise the equilibrium magnetisation state by counteracting magnetic relaxation. Here, we maximise 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 stabilisation of the magnetisation in the direction opposite to an applied magnetic field, thereby realising a spintronic analogue of the Kapitza pendulum. In an intermediate current regime, the STT drives large magnetisation vector fluctuations that cover the entire Bloch sphere. The continuous variable associated with the stochastic magnetisation 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.