The present work focuses on the unique ability of magnetic small-angle neutron scattering (SANS) to quantitatively analyze the magnetic interactions, namely the exchange-stiffness constant and the strength and spatial structure of the magnetic anisotropy and magnetostatic fields in (Fe0.7Ni0.3)86B14 alloy . This particular compound is a promising HiB-NANOPERM-type soft magnetic nanocrystalline material, which exhibits an ultrafine-grained microstructure with an average particle size as small as 4 nm and an extremely small coercive field of ~ 4.9 μT. The neutron data analysis based on the micromagnetic SANS theory yields an exchange-stiffness constant of Aex = (10 ± 1) × 10-12 J/m, a value that is 2-3 times larger than those reported previously for similar alloys . The large value of Aex together with the small grain size and low anisotropy is believed to be responsible for the extreme magnetic softness of this alloy. Furthermore, the magnitude of the extracted anisotropy-field and longitudinal magnetization scattering functions allow us to conclude that the magnetization jumps at internal particle-matrix interfaces, and the ensuing dipolar stray fields, are the main source of the spin disorder in this material.
This work was financially supported by the National Research Fund of Luxembourg (AFR grant No. 15639149 and CORE grant SANS4NCC).
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