Evaluating the effect of Mn composition on chemical partitioning in Co(78−x)Fe2MnxB14Si2Nb4 magnetic amorphous nanocomposites

Highlights: • HR-TEM and APT data series in Co_(78−x)Fe₂Mn_xB₁₄Si₂Nb₄. • Mn content increases crystallinity of Co(Fe)-rich phases. • Mn content increases mobility mechanisms influencing nucleation rate. -- Abstract: We report the chemical partitioning behavior in a series of melt spun, partially crystallized Co_(78−x)Fe₂Mn_xB₁₄Si₂Nb₄ (x = 0.5, 2.0, 4.0, and 6.0) alloys. Upon annealing at 520 °C anneal for 20 min, 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.