Magnetic Stochastic Resonance

General Physics Institute of Russian Academy of Science

MAGNETOSTOCHASTIC RESONANCE

1. Essence of the phenomenon

Magnetostochastic resonance (MSR) is a new effect of a sharp rise of a bistable system response to external fields in the presence of noise due to tunnelling of magnetic moment between energy minima. The system response to a weak harmonic force is determined by a local stiffness of an energy minimum in which the system is located. In the presence of noise (a random force inducing system transitions between minima) the response of a system is defined by an effective stiffness of a potential, which can be much smaller than the local stiffness of a minimum. Thus, an addition of noise in a bistable system can result in an enhancement of the system response to periodic modulation and in an increase of the signal-to-noise ratio.

2. Object of researches

Objects of researches are various bistable magnetic systems that include nanoparticles of magnetic materials, uniaxial ferrite-garnet thin films and local parts of domain walls. In experiments the response of a local part of domain wall to an external harmonic magnetic field in the presence of a random magnetic field was measured.

3. Main scientific results.

The phenomenon of magnetostochastic resonance in a uniaxial ferromagnetic material was predicted. MSR is experimentally found and investigated in dynamics of magnetization in thin ferrite-garnet films and ultrafine powders of iron oxides. A strong dependence of a MSR signal upon symmetry of a bistable potential was found. It was shown that the quenching of the response to periodic forces caused by a constant field can be used for evaluation of the fluctuation strength in a bistable system.

For the first time the dynamics of a bistable system subject to several periodic forces and noise was investigated both experimentally and theoretically. It was shown that the mixed harmonics, which arises under the action of two periodic forces in the presence of noise, demonstrate the stochastic resonance behaviour. A dependence of signals on first and mixed harmonics upon the constant field that makes energy minima unequal was investigated. It was shown that this dependence has a scale of changes proportional to the noise strength. The harmonic symmetry and parameters of their changes were found in a qualitative agreement with the developed theory.

It was shown that stochastic resonance on higher harmonics has a bigger quality and a wider area of applications than that on the first harmonic and can be observed in various types of monostable systems. For the first time MSR on the third harmonic in a monostable magnetic potential was experimentally found.

The conducted researches result in an opportunity of an evaluation of fluctuation parameters of bistable systems (the fluctuation strength) through measurements of the system response to periodic modulation (response changes due to the constant field that makes minima unequal).

MSR can be used for investigations of macroscopic quantum tunnelling of magnetic moment and spin depended tunnelling currents.

MSR in magnetic nanoparticles can be applied for development of magnetic field sensors with the frequency bandwidth up to 1 GHz, which can study magnetic field of nanoobjects and sub-threshold signals.

4. Support.

The research was supported by

Soros Foundation, Grant No. M8L000 and M8L300

INTAS Grant No. 94-1720

RFBR Grant No. 96-02-18956

References

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