V. DeGeorge

Induced anisotropy in FeCo-based nanocomposites: Early transition metal content dependence

Soft magnetic nanocomposites variants of FeCo-based (HTX002) alloys (Fe65Co35)81+xB12Nb4−xSi2Cu1, exhibiting high inductions (up to 1.9 T), low losses, and high temperature stability are studied for high frequency inductors and current sensors. For alloys with x = 0, 1, 1.5, 2, and 3, we report field induced anisotropy, KU, after annealing at temperatures of 340–450 °C for 1 h in a 2 T transverse magnetic field. The anisotropy field, HK, measured by AC permeametry on toroidal cores, and by first order reversal curves on square sections of ribbon, decreases with annealing temperature and saturates at high annealing temperatures suggesting a nanostructure related anisotropy mechanism in which the amorphous phase exhibits a higher HK than the crystalline phase. A high saturation induction nanocrystalline phase and high HK amorphous phase were achieved by low temperature annealing resulting in a value of KU exceeding 14 × 103 erg/cm3, more than twice that reported previously for Fe-rich amorphous and nanocomp...

High speed electric motors based on high performance novel soft magnets

Novel Co-based soft magnetic materials are presented as a potential substitute for electrical steels in high speed motors for current industry applications. The low losses, high permeabilities, and good mechanical strength of these materials enable application in high rotational speed induction machines. Here, we present a finite element analysis of Parallel Path Magnetic Technology rotating motors constructed with both silicon steel and Co-based nanocomposite. The later achieved a 70% size reduction and an 83% reduction on NdFeB magnet volume with respect to a similar Si-steel design.

Mass Balance and Atom Probe Tomography Characterization of Soft Magnetic (Fe 65 Co 65 ) 79.5 B 13 Si 2 Nb 4 Cu 1.5 Nanocomposites

Electric and magnetic properties, including saturation induction, resistivity, Curie temperature, and others, that make soft magnetic materials attractive for applications such as power converters and electric machines depend on local alloy composition. In this paper, we address this dependence quantifiably. First, we correlate the crystallization state to local composition with a novel mass balance. Second, we perform atom probe tomography on (Fe65Co35)79.5B13Si2Nb4Cu1.5 magnetic nanocomposites to explore local compositional evolution with devitrification and test predictions. Precise 3-D atom maps of constituent elements are constructed from as-cast, intermediate, and late stage crystallized samples. Local compositions and final crystal fraction predicted from mass balances are tested. Analysis of chemical partitioning during growth quantifies the depletion of glass formers (GFs) in nanocrystals, and enrichment of GFs and depletion of Fe and Co in the amorphous phase. Finally, we demonstrate the direct measurement of local composition on a nanometer scale and present predictive models necessary to deduce intrinsic constituent phase properties and investigate the proposed shell interfacial phases.

Structure–Property Correlations in CoFe–SiO 2 Nanogranular Films Utilizing x-Ray Photoelectron Spectroscopy and Small-Angle Scattering Techniques

A quantitative structure–property correlation study of thin films consisting of CoFe nanoparticles embedded in SiO2 is presented, comparing film microstructure and chemistry with measured magnetic properties. SiO2 was fully percolated for all films with > ~50% SiO2 by volume, and decreasing CoFe-nanoparticle size and separation with increasing SiO2 resulted in a transition to superparamagnetic behavior. Partial oxidation of transition-metal elements is observed by x-ray photoelectron spectroscopy, and evidence for interparticle magnetic interactions can be resolved in soft x-ray resonant small-angle scattering experiments, highlighting the need for additional detailed and quantitative studies in this class of soft magnetic materials.

Time temperature transformation diagram for secondary crystal products of Co-based Co-Fe-B-Si-Nb-Mn soft magnetic nanocomposite

Secondary crystallization is the subject of much investigation in magnetic amorphous and nanocomposites (MANCs) as it limits the long term and thermal stability of their operation in device applications, including power electronics, sensors, and electric motors. Secondary crystal products [Blazquez et al., Philos. Mag. Lett. 82(7), 409–417 (2002); Ohodnicki et al., Phys. Rev. B 78, 144414 (2008); Willard et al., Metall. Mater. Trans. A 38, 725 (2007)], nanostructure and crystallization kinetics [Hsiao et al., IEEE Trans. Magn. 38(5), 3039 (2002); McHenry et al., Scr. Mater. 48(7), 881 (2003)], and onset temperatures and activation energies [Ohodnicki et al., Acta. Mater. 57, 87 (2009); Long et al., J. Appl. Phys. 101, 09N114 (2007)] at constant heating have been reported for similar alloys. However, a time-temperature-transformation (TTT) diagram for isothermal crystallization, more typical of application environments, has not been reported in literature. Here, a TTT diagram for the Co based, Co-Fe-Si-Nb-...