Correlating microstructural features with magnetic domains in (MnFeCoNiCu)100−xAlxsoft magnets via advanced electron microscopy

Abstract

We explore the influence of microstructures on the soft magnetic and mechanical properties of the multi-principal element alloys (MPEAs), (MnFeCoNiCu)100−xAlx (x = 20, 25, 30, 35, 40 at.%). Our investigation reveals that the addition of Al promotes a microstructural change from a coexistence of face-centered cubic (FCC), body-centered tetragonal (BCT), and B2 phases to a single B2 phase. The microstructure is characterized by micron-scale FCC precipitates embedded within the B2 matrix. The (MnFeCoNiCu)75Al25 alloys exhibit high saturation magnetization (MS = 105.5 Am2/kg at T = 100 K), low coercivity (HC = 8.7 A/m), high Curie temperature (TC = 732 K), and high Vickers hardness of 513 HV. Lorentz TEM reveals that the B2 phase is a ferromagnetic phase with a domain wall width of 64 ± 3 nm, and the FCC phase is a non-ferromagnetic phase. We find that the FCC nano-precipitates are coherently interfaced with the B2 matrix. Due to their small size (< 20 nm), they do not act as pinning centers. Our work reveals that the direct correlation of magnetic properties with microstructural characteristics is discussed in light of the structure and phase composition changes observed for different aluminum content, and provides valuable guidance for material optimization.

Keywords

• Microstructural characteristics
• Soft-magnetic properties
• Lorentz TEM
• Multi-principal element alloys