Influence Of Nb-doping And Current Annealing On Giant Magnetoimpedance Effect Of Co-based Metallic Microfibers

Co-based metallic microfibers have been attracted much attention because of their excellent gaint magnetoimpedance effect(GMI).In this paper,Co-Fe-Si-B-Nb series metallic microfibers were prepared by rotated dipping process.The effects of Nb-doping amount and current annealing process on the GMI effect of metallic microfibers were investigated systematically,and the influence mechanism of different modulation treatments on GMI properties was discussed.That is,the transient temperature rise characteristics of Nb-doped Co-based metallic microfibers during DC and AC annealing were analyzed by numerical calculation to determined the current annealing process parameters,and then current modulation treatment is carried out.At the same time,the microstructure of Co-based metallic microfibers before and after annealing was characterized by XRD,DSC,SEM and TEM,respectively.The magnetic property measurement system(MPMS)was used to measure the general magnetic properties of Co-based metallic microfibers,and the magnetoimpedance properties were analyzed by magnetoimpedance comprehensive testing platform to further clarify the electromagnetic coupling mechanism.The experimental results show that Co-based metallic microfibers are typical amorphous structure and exhibit favorable glass-forming ability and thermal stability.A small content of Nb-doping can improve the thermal stability and the degree of structural order(?)of the metallic microfibers are increased,meanwhile,a certain amount of nanoclusters appear on the amorphous matrix,which is more conducive to improve the magnetic properties of the metallic microfibers.Among them,the saturation magnetization of Co Fe Si BNb1 metallic microfibers is the highest,up to78.74 emu/g.Meanwhile,the maximum impedance change rate[?Z/Z_max]_max and the maximum magnetic field response sensitivity?_max increase at first and then decrease with the increase of Nb doping.Among them,the giant magnetoimpedance of Co Fe Si BNb2 microfibers is better,and its[?Z/Z_max]_max and?are 206.80%and29.23%/Oe,separately.After doping Nb element instead of B element,the permeability of Co-based metallic microfibers increases and the micro-area magnetic anisotropy increases.Simultaneously,the negative or near-zero magnetostriction coefficient induces the formation of a more regular circumferential magnetic domain structure in the metallic microfibers,and the GMI effect is improved.Current modulation treatment can improve the general magnetic properties and GMI effect of Nb-doped Co-based metallic microfibers.Among them,the 90 m A&50Hz DC annealed microfibers has better magnetoimpedance properties,when f=1MHz,its[?Z/Z_max]_max,?_max,H_k,H_p are 213.08%,41.76%/Oe,0 Oe and 1 Oe;140 m A&50Hz AC annealed microfibers have better magnetoimpedance properties,when f=1MHz,its[?Z/Z_max]_max,?_max,H_k,H_p are 213.15%,31.04%/Oe,1 Oe and 2 Oe,respectively.AC current frequency can also improve the GMI effect of metallic microfibers.The current modulation treatment can effectively eliminate the residual stress in the metallic microfibers and improve the atomic relaxation state.In the meantime,it can also produce the ordered micro-region of the atomic array,and the ordered degree of the AC annealed fiber structure?is 29.69%.On the other hand,current modulation treatment can produce a stable circumferential magnetic field,which can adjust the distribution of microfibers magnetic domain structure when stress releasing,significantly increase the circumferential permeability and enhance the induced magnetic anisotropy,thus improving the magnetoimpedance effect.