Abstract
We report on the design and observation of huge inverse magnetizations pointing in the direction opposite to the applied magnetic field, induced in nano-sized amorphous Ni shells deposited on crystalline Au nanoparticles by turning the applied magnetic field off. The magnitude of the induced inverse magnetization is very sensitive to the field reduction rate as well as to the thermal and field processes before turning the magnetic field off, and can be as high as 54% of the magnetization prior to cutting off the applied magnetic field. Memory effect of the induced inverse magnetization is clearly revealed in the relaxation measurements. The relaxation of the inverse magnetization can be described by an exponential decay profile, with a critical exponent that can be effectively tuned by the wait time right after reaching the designated temperature and before the applied magnetic field is turned off. The key to these effects is to have the induced eddy current running beneath the amorphous Ni shells through Faraday induction.
Highlights
It is known that a time-varying magnetic field can be used to generate an electric current in conducting materials
We report on the design and observation of huge inverse magnetizations induced by Faraday induction in 2.2 nm thick amorphous Ni shells deposited on 2.4 nm crystalline Au
This structure of a nano-sized amorphous Ni shell deposited on a crystalline Au nanoparticle in the core can further be developed into a nano-magnetic switch, when is using the on-or-off of an external magnetic field to change the magnetic polarization of the structure that switching the connection from one loop to the other
Summary
It is known that a time-varying magnetic field can be used to generate an electric current in conducting materials. As stated in Lenz’s law, the magnetic field of the induced eddy current is opposite to the change in the external magnetic field The generation of such eddy currents in conducting materials is technologically important and has useful practical applications. The magnetic material in the amorphous structure has an extremely low magnetic anisotropy energy, so that the directions of hard and easy magnetizations are largely relaxed All these properties are technologically valuable for applications as a soft magnetic material and could be used to tune the behavior. We report on the design and observation of huge inverse magnetizations induced by Faraday induction in 2.2 nm thick amorphous Ni shells deposited on 2.4 nm crystalline Au. NPs cores, marked Au@Ni (core@shell). Inverse magnetization was obtained by placing the amorphous Ni in such a way that the eddy current circulated beneath the amorphous Ni shell
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