Bifurcation and chaos in spin-valve pillars in a periodic applied magnetic field

TL;DR

This paper investigates how a periodically varying magnetic field can induce bifurcation and chaos in the magnetization dynamics of spin-valve pillars, offering a more feasible experimental approach compared to spin-current modulation.

Contribution

It demonstrates that chaotic behavior in spin-valve systems can be achieved through applied magnetic fields, not just spin-current variations, and explores effects of crystal anisotropy on chaos onset.

Findings

Chaotic dynamics can be induced by periodic magnetic fields with constant spin current.

Chaos occurs at lower field magnitudes when crystal anisotropy is present.

The approach simplifies experimental realization of chaos in spintronic devices.

Abstract

We study the bifurcation and chaos scenario of the macro-magnetization vector in a homogeneous nanoscale-ferromagnetic thin film of the type used in spin-valve pillars. The underlying dynamics is described by a generalized Landau-Lifshitz-Gilbert (LLG) equation. The LLG equation has an especially appealing form under a complex stereographic projection, wherein the qualitative equivalence of an applied field and a spin-current induced torque is transparent. Recently chaotic behavior of such a spin vector has been identified by Zhang and Li using a spin polarized current passing through the pillar of constant polarization direction and periodically varying magnitude, owing to the spin-transfer torque effect. In this paper we show that the same dynamical behavior can be achieved using a periodically varying applied magnetic field, in the presence of a constant DC magnetic field and constant spin current, which is technically much more feasible, and demonstrate numerically the chaotic dynamics in the system for an infinitely thin film. Further, it is noted that in the presence of a nonzero crystal anisotropy field chaotic dynamics occurs at much lower magnitudes of the spin-current and DC applied field.