Relaxation time and critical slowing down of a spin-torque oscillator

Abstract

The relaxation phenomena of spin-torque oscillators consisting of nanostructured ferromagnets are interesting research targets in magnetism. A theoretical study on the relaxation time of a spin-torque oscillator from one self-oscillation state to another is investigated. By solving the Landau-Lifshitz-Gilbert equation both analytically and numerically, it is shown that the oscillator relaxes to the self-oscillation state exponentially within a few nanoseconds, except when magnetization is close to a critical point. The relaxation rate, which is an inverse of relaxation time, is proportional to the current. On the other hand, a critical slowing down appears near the critical point, where relaxation is inversely proportional to time, and the relaxation time becomes on the order of hundreds of nanoseconds. These conclusions are primarily obtained for a spin-torque oscillator consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer, and are further developed for application to arbitrary types of spin-torque oscillators.

arXiv comment13 pages, 7 figures

References in corpus (16)

• Microwave Oscillations of a Nanomagnet Driven by a Spin-Polarized Current
• Spin torque building blocks
• Currents, Torques, and Polarization Factors in Magnetic Tunnel Junctions
• Current-Driven Microwave Dynamics in Magnetic Point Contacts as a Function of Applied Field Angle
• Spin-torque switching: Fokker-Planck rate calculation
• Spin Transfer Dynamics in Spin Valves with Out-of-plane Magnetized CoNi Free Layers
• Thermally activated switching of perpendicular magnet by spin-orbit spin torque
• Critical Field of Spin Torque Oscillator with Perpendicularly Magnetized Free Layer
• Spin torque switching of an in-plane magnetized system in a thermally activated region
• Spin Torque Oscillators with Thermal Noise: A Constant Energy Orbit Approach
• Large amplitude microwave emission and reduced nonlinear phase noise in Co2Fe(Ge0.5Ga0.5) Heusler alloy based pseudo spin valve nanopillars
• Instability analysis of spin torque oscillator with an in-plane magnetized free layer and a perpendicularly magnetized pinned layer
• Averaged equation for energy diffusion on a graph reveals bifurcation diagram and thermally assisted reversal times in spin-torque driven nanomagnets
• Magnetization switching by current and microwaves
• Nonlinear analysis of magnetization dynamics excited by spin Hall effect
• Stable oscillation in spin torque oscillator excited by a small in-plane magnetic field

Cited by in corpus (6)

• Synchronization and chaos in a spin-torque oscillator with a perpendicularly magnetized free layer
• Chaos in nanomagnet via feedback current
• Synchronized, periodic, and chaotic dynamics in spin torque oscillator with two free layers
• Spin-current driven spontaneous coupling of ferromagnets
• Indirect excitation of self-oscillation in perpendicular ferromagnet by spin Hall effect
• Spin Torque Oscillations Triggered by In-plane Field