Static magnetic field modulates spinodal decomposition in CuNiFe system
Date:
Contributed poster at the 2022 Institute of Physics Theory of Condensed Matter (TCM) Group conference.
Abstract
Electric machines with improved efficiency and performance require ferromagnetic materials with optimized structures and properties, which are sensitive to specific aspects of material processing. In this study, structural and magnetic attributes of the spinodal alloy CuNiFe subjected to magnetic-field-assisted annealing are investigated from combined experimental and computational perspectives. We demonstrate that the application of a mild, static magnetic field during thermal treatment promotes spinodal elemental redistribution in the alloy, impacting the resulting phase distribution, scale, and extrinsic magnetic response.
Ribbons of composition Cu40Ni42Fe18 were synthesized by melt-spinning into a uniform, FCC-structured, soft magnetic solid solution phase and were subsequently annealed at 500°C for up to 200 hours with or without a mild magnetic field (µ0H = 60 mT) . All annealed specimens exhibit nanoscale (~10 nm) periodic chemical segregations into Cu-rich and FeNi-rich regions within a coherent FCC lattice along <100> direction, with the wavelength and amplitude of the chemical periodicity increasing with annealing time. This spinodal decomposed structure results in increased magnetic hardness. It is found that magnetic field annealing modulates spinodal structure by promoting the amplitude of chemical fluctuations up to three-fold, consistent with enhanced diffusional fluxes during decomposition, resulting in higher coercivity and lower initial susceptibility relative to the zero-field-annealed counterparts. Contributing fundamental insight into these outcomes, first-principles DFT calculations suggest that long-range ferromagnetic order induced by an external magnetic field substantially alters the strength and nature of atomic interactions, impacting the stability of the initial solid solution phase. These results suggest that annealing with engineering-approachable magnetic fields can achieve controlled microstructures of alloys, resulting in modified magnetic anisotropy and responses.