NOVELTY - A nanocomposite comprises a nonmetallic polymer matrix; and several magnetic nanoparticles evenly dispersed throughout the polymer matrix.    USE - As nanocomposite (claimed) in fuel cell application; for urethane polymerization; in computing, storage and magnetic field sensing devices; in thin film applications; in sensor applications; in applications such as specific molecular targeting; in magnetic data storage (hard disk), biological detection, magnetic recording and rotational sensing in automotive systems; and in electromagnetic applications.    ADVANTAGE - The nanocomposite has good giant magnetoresistance (GMR) characteristics and structural integrity. The nanocomposite can be manufactured by inexpensive process; does not require complex preparation and packaging steps; shows improved performance characteristics; and is simple to manufacture thus enabling near-term practical applications. Compared with metallic GMR structure, polymer nanocomposite GMR structures have benefits of superior structural integrity. The nanocomposites can be involved in sensor applications in harsh environment; and in applications such as specific molecular targeting due to the multifunctional groups of the polymer matrix. The high loading of nanoparticles in polymer matrix makes the GMR sensors a suitable replacement for current magnetic thin film or granular structured GMR sensors.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) method (M1) of fabricating nanocomposite involving activating the surfaces of several metal nanoparticles having a metal core and an oxide shell with a promoting agent to form an activated mixture; combining the activated mixture with at least one monomer and at least one solvent; polymerizing the combined activated mixture, monomer and solvent to form a polymerized nanocomposite; and drying the polymerized nanocomposite;    (2) method (M2) of fabricating nanocomposite involving blending several metal nanoparticles with at least one monomer in an inert environment using energetic mixing; mixing a promoter with the blended nanoparticles and monomer to form a polymerized nanocomposite; and drying the nanocomposite;    (3) method (M3) of fabricating a nanocomposite involving: dissolving at least one polymer in an anhydrous, organic solvent; mixing metal nanoparticles into the polymer solution using energetic mixing; separating solid and liquid phases with a polar solvent; filtering and drying the solid phase; and reacting the solid phase in reducing environment to form carbon fibers; and    (4) method (M4) of fabricating a nanocomposite involving: dispersing metal nanoparticles and at least one monomer in an anhydrous, anoxic solvent to provide a dispersed solution; applying an electrochemical potential to the dispersed solution; and forming a thin film on an anode electrode structure.