Magnetization dynamics in a dual free-layer spin-torque nano-oscillator

We report micromagnetic simulations of magnetization dynamics in a spin-torque nano-oscillator (STNO) that consists of two in-plane free-layers located between two fixed out-of-plane polarizers. In the optimal regime of the STNO operation, the free-layers process opposite one another on large- ampli...

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Bibliographic Details
Published in:Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2012-09, Vol.86 (9), Article 094425
Main Authors: Rowlands, Graham E., Krivorotov, Ilya N.
Format: Article
Language:English
Subjects:
Dynamics
Fluid flow
Formations
Joining
Magnetization
Nanostructure
Simulation
Vortices
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Summary:We report micromagnetic simulations of magnetization dynamics in a spin-torque nano-oscillator (STNO) that consists of two in-plane free-layers located between two fixed out-of-plane polarizers. In the optimal regime of the STNO operation, the free-layers process opposite one another on large- amplitude out-of-plane trajectories and generate large microwave power at the sum of their precession frequencies. Our simulations reveal that the frequency band of the STNO operation can be severely limited by formation of a static magnetic vortex in the free-layers, and that the bandwidth can vanish in commonly used free-layer materials such as Permalloy. We show that the vortex formation can be suppressed and the bandwidth significantly extended by increasing Gilbert damping in the free-layers and minimizing coupling between the free-layers by means of interlayer exchange interaction. We explore the operation of the STNO with and without the inclusion of the spin-torque coupling between the two free-layers. Our simulations demonstrate that an STNO with dual free-layers is a promising candidate for the development of high-power high-frequency STNOs operating in the absence of an external magnetic field.
ISSN:1098-0121
1550-235X
DOI:10.1103/PhysRevB.86.094425