Investigations into Structural, Magnetic, and Chemical Properties of Magnetic Metal-Amorphous Nanocomposites

Metal-amorphous nanocomposites (MANCs) are currently seeing rigorous researchleading to the development of cleaner and more efficient materials for power applications.This dissertation reports on three topics related to MANCs, namely the stability ofnanocrystalline Co, magnetic properties derived from nano/microstructures usingmicromagnetic simulations, and the chemical partitioning characteristics in MANCs usingatom probe tomography (APT). Density functional theory was used to determine the influence of Mn doping on thestructural and magnetic behavior of face-centered cubic (FCC) Co. Prior reports show thatMn doping can have a tremendous impact on the permeability of Co-based MANCs. Here,it was found that the quantity and location of Mn atoms within the FCC Co supercellinfluence the local magnetic moments and can result in structural faulting in Co. Since a MANC is composed of nanocrystallites in an amorphous matrix, a Voronoitessellation construction method was implemented to create realistic representations ofthese nano/microstructures for micromagnetic simulations. The results reveal adependency of the coercivity response on the crystallite size, ?, and the crystallite volumefraction, with lower fractions deviating from established ?^(3−6) dependencies. Finally, APT studies examined how early transition metals in Fe-based MANCspartition to mitigate crystallite growth enabling MANCs to operate in warmerenvironments, such as engines. Using Ta, rather than Nb, is shown to increase the thermalstability of such materials. The APT studies conducted indicate that there is a reducedpartitioning of Fe out of the matrix of the MANC when Ta is used, showing that thisthermal stability is affected by partitioning.