Microtech 2011

Magnetic nanoparticles as components of magnetoresistance sensors: the gGMR-sensor

A. Weddemann, I. Ennen, A. Regtmeier, A. Hütten, M. Zahn
Massachusetts Institute of Technology, US

Keywords: magnetic nanoparticles, granular GMR, magnetoresistive sensor


Superparamagnetic microbeads and nanoparticles have a wide range of applications. Due to their magnetic stray field they influence soft magnetic material nearby which allows for the magnetic recognition of such particles by magnetoresistive sensors. Such sensors consist of various layers with a soft ferromagnetic top electrode which acts as a sensing element. Downscaling these sensor devices below the micron size results in a high magnetic stiffness; sensor elements are no longer sensitive to small field variations which is one of the major challenges when designing magnetoresistive sensors below the micron size. By the employment of assemblies of superparamagnetic particles, the confinement is broken by spatial separation: Each particle in such an arrangement forms its own magnetic domain which couples to particles nearby via their stray fields entailing a magnetic superstructure of antiferromagnetic domains. Due to spin-dependent transport phenomena, such a particle sheet may serve as a granular giant magnetoresistance sensor capable of monitoring magnetic sources. We analyze the employability of this approach for the design of novel magnetoresistance sensors. It will be shown that the increase of sensitivity due to local switching is bought at the cost of inherent device noise.

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