Optimal switching of a nanomagnet assisted by microwaves

Abstract

We develop an efficient and general method for optimizing the microwave field that achieves magnetization switching with a smaller static field. This method is based on optimal control and renders an exact solution for the 3D microwave field that triggers the switching of a nanomagnet with a given anisotropy and in an oblique static field. Applying this technique to the particular case of uniaxial anisotropy, we show that the optimal microwave field, that achieves switching with minimal absorbed energy, is modulated both in frequency and in magnitude. Its role is to drive the magnetization from the metastable equilibrium position towards the saddle point and then damping induces the relaxation to the stable equilibrium position. For the pumping to be efficient, the microwave field frequency must match at the early stage of the switching process the proper precession frequency of the magnetization, which depends on the magnitude and direction of the static field. We investigate the effect of the static field (in amplitude and direction) and of damping on the characteristics of the microwave field. We have computed the switching curves in the presence of the optimal microwave field. The results are in qualitative agreement with micro-SQUID experiments on isolated nanoclusters. The strong dependence of the microwave field and that of the switching curve on the damping parameter may be useful in probing damping in various nanoclusters.

9 pages, 8 figures

References in corpus (2)

• Quantum optimal control theory and dynamic coupling in the spin-boson model
• Magnetization reversal and nonexponential relaxation via instabilities of internal spin waves in nanomagnets

Cited by in corpus (18)

• Magnetization reversal condition for a nanomagnet within a rotating magnetic field
• Reversal of magnetization of a single-domain magnetic particle by the ac field of time-dependent frequency
• Autoresonant control of the magnetization switching in single-domain nanoparticles
• Magnetization switching by current and microwaves
• Microwave-assisted switching of a nanomagnet: analytical determination of the optimal microwave field
• Spin torque oscillator for microwave assisted magnetization reversal
• Optimal control of magnetization reversal in a monodomain particle by means of applied magnetic field
• Optimal protocol for spin-orbit torque switching of a perpendicular nanomagnet
• Subnanosecond magnetization reversal of magnetic nanoparticle driven by chirp microwave field pulse
• Thermally assisted magnetization reversal of a magnetic nanoparticle driven by a down-chirp microwave field pulse
• Fast magnetization reversal of a magnetic nanoparticle induced by cosine chirp microwave field pulse
• Magnetization switching by microwaves initially rotating in opposite direction to precession
• Optimal state transfer of a single dissipative two-level system
• Reduction of energy cost of magnetization switching in a biaxial nanoparticle by use of internal dynamics
• Transition state theory characterizes thin film macrospin dynamics driven by an oscillatory magnetic field: Inertial effects
• Shape anisotropy effect on magnetization reversal induced by linear down chirp pulse
• Transition state dynamics of a driven magnetic free layer
• Surface-induced reduction of the switching field in nanomagnets