Evaluating the Effect of Mn Composition on Chemical Partitioning in Co(78-x)Fe2MnxB14Si2Nb4 Magnetic Amorphous Nanocomposites

Abstract We report the chemical partitioning behavior in a series of melt spun, partially crystallized Co(78-x)Fe2MnxB14Si2Nb4 (x = 0.5, 2.0, 4.0, and 6.0) alloys. Upon annealing at 520°C anneal for 20 minutes, nanocrystallites precipitated from the amorphous matrix that have been previously reported to decrease the magnetic permeability with increasing Mn content. Transmission electron microscopy identified the crystallites within the continuous amorphous matrix as a mixture of hexagonal close packed and face centered cubic phases with an average size of 7.0 ± 3.0 nm. Atom probe tomography (APT) revealed an increase in chemical partitioning between the ferromagnetic and glass-forming elements upon annealing with the crystallite density increasing with Mn content. This implied an increase in crystallinity and a reduction of point defects (vacancies) that accompanied changes in Mn content during the chemical partitioning process, where the extent of crystallinity would influence magnetic properties.