Effect Of Longitudinal Magnetic Field Annealing On The Soft Magnetic Properties Of FeCo-based Nanocrystalline Alloys

The structure and magnetic properties of (Fe1-xCox) 78.4Si9BB9Nb2.6Cu1(x=0.35,0.5,0.65,1) alloys have been systematically studied in the dissertation. by nanocrystallization of amorphous precursors at various magnetic annealing . Effect of longitudinal magnetic field annealing on Static magnetic properties of the alloys with different Co content was mainly studied.The method of comparing longitudinal field anneal to No-field anneal was adopted in the experiments. No-field anneal and longitudinal field anneal have been carried out on the alloy of (Fe1-xCox) 78.4Si9BB9Nb2.6Cu1(x=0.35,0.5,0.65,1) at 410℃--560℃for 30min. Static magnetic properties of the alloys annealed under different conditions were studied by NIM-2000S measure system for soft magnetic material. We have recently demonstrated that annealing under a longitudinal magnetic field is effective in improving the magnetic softness of nanocrystalline alloys. The annealing of the alloys in the presence of longitudinal magnetic field results in a rectangular shape of hysteresis loops, maximal permeability is enhanced and the coercivity of nanocrystalline is reduced.Under the influence of magnetization induced by the applied field a preferential alignment of atom pairs is developed. The preferential alignment of atom pairs constitutes a"directional order", which make the magnetic domain align in the direction of the applied magnetic field,so little magnetic domain align in the direction normal to the field. Then the uniaxial anisotropy is induced, who's easy axial is in the direction of the magnetic field, and the magnetic properties of alloys is improved. With increasing of Co content, more Fe-Fe, Co-Co atom pairs are developed so that the coercive force Hc is enhanced drastically.The high-temperature soft magnetic properties are studied by means of the temperature evolution of initial permeability. Whether adding a field to a treatment or not had do nothing to do with initial permeability at low temperature. But above 500℃, the temperature of the peak of initial permeability would become low comparing to No-field annealing.The remanence-to-saturation ratio Br/Bs of alloys annealing in different magnetic field were analyzed. The results show that when the Co content x=0.5, the BBr/Bs value is bigger then others, which matches the theory of Neel-Taniguchi about the directional ordering of the atom pairs, so it's concluded that the anaxial anisotropy is the more important factor of the drastic changes in the magnetic properties.