Magnetoresistive (MR) sensors have been identified as promising candidates for the development of high-performance magnetometers due to their high sensitivity, low cost, low power consumption, and small size. The rapid advance of MR sensor technology has opened up a variety of MR sensor applications. These applications are in different areas that require MR sensors with different properties. Future MR sensor development in each of these areas requires an overview and a strategic guide. A MR sensor roadmap (non-recording applications) was therefore developed and made public by the Technical Committee of The IEEE Magnetics Society with the aim to provide an R&D guide for MR sensors intended to be used by industry, government, and academia. The roadmap was developed over a three-year period and coordinated by an international effort of 22 taskforce members from 10 countries and 17 organizations, including universities, research institutes, and sensor companies. In this paper, the current status of MR sensors for non-recording

Polyaniline nanospheres (PANI-NS) prepared by morphological transformation of micelle polymerized camphorsulfonic acid (CSA) doped polyaniline nanotubes (PANI-NT) in the presence of ethylene glycol (EG) have been characterized by X-ray diffraction, atomic force microscopy, transmission electron microscopy, scanning electron microscopy, Fourier transform infra-red and UVVisible spectroscopy. A PANI-NS (60-80 nm) film deposited onto an indium-tin-oxide (ITO) coated glass plate by the solution casting method has been utilized for covalent immobilization of biomolecules (cholesterol oxidase (ChOx)) via N-ethyl-N 0 -(3-dimethylaminopropyl) carbodiimide (EDC) and Nhydroxysuccinimide (NHS) chemistry for fabrication of a cholesterol biosensor. The ChOx/PANI-NS/ ITO bioelectrode detects cholesterol in the concentration range of 25 to 500 mg dL À1 with sensitivity of 1.3 Â 10 À3 mA mg À1 dL and regression coefficient of 0.98. Further, this PANI-NS based bioelectrode shows fast response time (10 s), low Michaelis-Menten constant (2.5 mM) and shelf-life of 12 weeks. The spherical nanostructure observed in the final morphology of the PANI-NS film is attributed to hydrogen bonding interactions between PANI-NT and EG.

The giant magnetoimpedance (GMI) has been measured in weak-field-annealed Co-based amorphous ribbon as functions of both the annealing field, Ha, and the measuring frequency. The GMI profile measured at 0.1 MHz shows a typical two-peak behavior for the sample with Ha less than 50 mOe. The GMI peak in the region where the applied field is antiparallel to the annealing field decreases with Ha, showing an asymmetry in the GMI profile. Eventually, the GMI peak in the antiparallel-field region disappears, and a drastic step-like change in the GMI peak is revealed for an applied field which is parallel to the annealing field of 500 mOe. The asymmetric GMI phenomenon for the 0.1 MHz measuring frequency, the so-called “GMI valve,” is due to a peculiar domain structure, which occurs in the sample surface during the field annealing. The GMI peak in the parallel-field region appears again for measuring frequencies over 0.5 MHz due to the remarkable contribution of the magnetization rotation to the GMI.

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The asymmetric giant magnetoimpedance (GMI) profile has been realized in weak-field-annealed Co-based amorphous ribbon at the annealing temperature of 380 °C in open air. Asymmetric GMI profiles with respect to applied field become profound as the annealing field increases over 500 mOe. The asymmetric GMI profile at the frequencies of ac current over 0.5 MHz is well ascribed for by the rotational transverse magnetization of single domain under a uniaxial anisotropy in amorphous core and a unidirectional anisotropy due to the exchange coupling with the bias field in the crystalline layer, underlying surface oxidation layer developed during the annealing in open air.