Magnetic Properties And Microstructure In Fe-based Metallic Glasses And Nanocrystalline Alloys

Metallic glasses?MGs?with disordered structure are obtained by quenching from highly viscous liquid and in a state of non-equilibrium state,so there is no long-range order in MGs and MGs could be characterized by short-range order.In the MGs the absence of long-range order leads to the absence of magnetocrystalline anisotropy,presenting high magnetoelastic-coupling coefficient.So their magnetic properties and magnetic domain structure are largely determined by anisotropy induced by stress.On these accounts,the influences of the stress on the magnetic properties of magnetic MGs are investigated widely.In this dissertation,focusing on the Fe-based MG ribbons under the bending deformation,the investigation on the stress relief of magnetic materials is important both for the industrial process and the academic research.In this work,the stress effects on the magnetic characteristics in Fe-based metallic glasses?MGs?are investigated under the applied bending stress and various annealing treatments.It was found that both the magnetic induction intensity B and effective permeability?'decrease while coercivity H_c increases with the applied compressive stress,indicating that the compressive effect is dominant on the magnetic characteristics in Fe₇₈Si₉B₁₃MG ribbons.We also found that the wide domain wall movement and the rotation of the narrow domains are seriously affected by internal stress during the magnetization process.Our results reveal that the stress relief plays a critical role in improving magnetic properties of Fe-based MGs and are helpful for understanding the correlations between the stress,microstructure change and magnetic softness in magnetic MGs.Fe-based metallic glasses?MGs?with excellent soft magnetic properties are applicable in a wide range of electronic industry.We show that the cryogenic thermal cycle has sensitive effect on soft magnetic properties of Fe₇₈Si₉B₁₃ glassy ribbon.The values of magnetic induction?or magnetic flux density?B and coercivity H_c show fluctuation with increasing number of thermal cycles.This phenomenon is explained as thermal cycle induced stochastically structural aging or rejuvenation which randomly fluctuates magnetic anisotropy and,consequently,the magnetic induction and coercivity.Overall,increasing the number of thermal cycles improves the soft magnetic properties of ribbon.The results could help understand the relation between relaxation and magnetic property,and the thermal cycle could provide an effective approach to improving performances of metallic glasses in industry.