Nonlinear dynamics of magnetization evolution in orthogonal spin torque devices: Phases and classification

Yuan Hui,Hao Yu,Zheng Yang

doi:10.1063/5.0031957

Abstract

The magnetization evolution of the free layer in an orthogonal spin torque device is studied based on a macrospin model. The trajectory of the magnetization vector under various conditions has shown rich nonlinear properties. The phase diagram is obtained in the parameter spaces of current density and the polarization distribution (the ratio of polarization of in-plane to out-of-plane layers), where two critical currents and three phases are found. These dynamic phases can be classified according to their nonlinear behaviors, which are different in terms of limit cycles and limit points. The classification is meaningful to design ultra-fast spin torque devices under different dynamic conditions toward various applications, such as in memory and oscillators.

Highlights

Spin-transfer torque (STT) discovered by Slonczewski and Berger1,2 is an effect that conductive electrons carrying angular momentum reorient the local spins, which enables the manipulation of magnetization by a spin-polarized current flowing through a multi-layered junction
The nonlinear phenomena suggest that we could classify the dynamic system in terms of its nonlinearity, such as limit cycle/limit point formed by the evolution trajectory of the magnetization vector. In this macrospin orthogonal spin torque (OST) model, we discovered that the dynamic process of magnetization evolves with horizontal equilibria bifurcation under particular conditions of current density and polarization distribution, which offers a reference to different applications
Phase 2 [Fig. 2(b)] shows the stage when the current density is enough for magnetization (J = 3 × 1011A/m2) where the free layer could achieve a reversal of my, namely, P to AP

Summary

Introduction

Spin-transfer torque (STT) discovered by Slonczewski and Berger1,2 is an effect that conductive electrons carrying angular momentum reorient the local spins, which enables the manipulation of magnetization by a spin-polarized current flowing through a multi-layered junction. In this macrospin OST model, we discovered that the dynamic process of magnetization evolves with horizontal equilibria bifurcation under particular conditions of current density and polarization distribution (the ratio of IP layer to OOP layer), which offers a reference to different applications.

Results

Conclusion