Giant Magneto-impedance Effect Of Amorphous Soft Magnetic Materials

As one of important branches in the sensor field, magnetic sensors play an important role in the modern human society, and they are indeed suitable for a large palette of applications such as transportation, mobile communications, space magnetic field reconnaissance, target detection, military, biomedical applications and so on, which almost permeate every corner of human daily life and industrial production. Nowadays, the popular magnetic sensors mainly include fluxgate, Hall-effect sensors, giant magnetoresistance（GMR） sensor, and SQUID, etc. However, the development potential of these magnetic sensors are severely limited due to their performance, scope and costs. So, in order to meet the demand for future social development, people are longing for a new kind of magnetic sensing technology to replace the traditional magnetic sensing technology. Until the 1990 s, the discovery of the giant magneto-impedance（GMI） effect brought a new dawn for the hope. Until now, the research objects of the GMI effect were gradually extended from the original Co-based amorphous wires to a variety of soft magnetic materials, including amorphous ribbons, thin films, multilayer films and composite structure wires. In the existing system of GMI materials, amorphous alloy have very excellent soft magnetic properties and good GMI effect, and thus it becomes the most important material system for the present research of the GMI effect.In this thesis, we studied the GMI effect of Fe_73.5Cu₁Nb₃Si_13.5B₉ and Co₆₅Ni₂Fe₄Si₁₅B₁₄ amorphous ribbons, respectively. On the one hand, we discussed the influence of different treatment methods on the GMI effect of amorphous materials in detail. Meanwhile, the appropriate treatment conditions were adopted to enhance the GMI effect and magnetic field sensitivity of amorphous ribbons. On the other hand, we directly used the aboved amorphous ribbon sample with high magnetic magnetic field sensitivity to detect the sign of Fe₃O₄ magntic nanoparticles, which could guide us to explore the applications of GMI effect in weak field detection and biological sensing. The main contents of this thesis are as follows:1. In this section, Fe_73.5Cu₁Nb₃Si_13.5B₉ amorphous ribbons are handled by direct current（DC） joule heat-treatment and rapid magnetic field heat-treatment, respectively. Firstly, the influence of DC amplitude and holding time on the GMI effect of Fe_73.5Cu₁Nb₃Si_13.5B₉ amorphous ribbon are carried out. The results indicate that the proper DC joule heat-treatment can dramatically enhance the GMI effect of Fe-based amorphous ribbons, which may be ascribed to the increasement of transverse permeability and the improvement of soft magnetic properties for as-cast ribbons. Secondly, a proper rapid heat-treatment can also improve the GMI effect of Fe-based amorphous ribbons, however, the enhancement of GMI effect really is inapparent. By applying a transverse magnetic field during the rapid heat-treatment process can improve the GMI effect of the asannealed ribbons further, it can be ascribed to the increasement of the transverse permeability.2. Different thickness of FeCo films were deposited on the surface of Fe_73.5Cu₁Nb₃Si_13.5B₉ amorphous ribbon by electroplating method, and thus forming the FeCo/amorphous ribbon/FeCo sandwich structure. We studied the influence of FeCo films thickness on the GMI effect of sandwich structure sample. The results indicated that the obviously enhanced GMI effect was obtained in sandwich structure sample, while the thin FeCo layer was deposited on the surface of Fe_73.5Cu₁Nb₃Si_13.5B₉ amorphous ribbon. With the increasing of FeCo film thickness, the GMI ratio of FeCo-coated ribbon firstly presents a significant drop and then tends to be stable. These results indicate that the appropriate thickness of FeCo coating film can enhance efficiently the GMI effect of amorphous ribbon.3. We studied the influence of tensile stress, dimension and geometry on the GMI effect of Co₆₅Ni₂Fe₄Si₁₅B₁₄ amorphous ribbons, respectively. Firstly, an enhanced GMI effect could be observed in amorphous ribbons after applying a tensile stress. And, with increasing the tensile stress value, the enhancement of the GMI effect in stretched amorphous ribbons would be more obvious. Secondly, the GMI effect of amorphous ribbon is highly affected by its width. The result shows that the max GMI ratio firstly increases and then decreases with the decrease of the amorphous ribbon width. In addition, the GMI effect of amorphous ribbon is also affected by its geometry. The magnetic field sensitivity of amorphous ribbon can be markedly improved by introducing a new structure, named as “sharp corner” structure.4. The surface shape anisotropy of Co₆₅Ni₂Fe₄Si₁₅B₁₄ amorphous ribbons was introduced by laser ablation, which can effectively influence the level and distribution of surface demagnetizing field for as-cast ribbons. On this basis, we discuss the influence of the direction of the laser etching on the GMI effect of Co-based amorphous ribbons. And, experiment results display that GMI ratio and magnetic field response sensitivity can be effectively regulated by this method.5. The weak magnetic signs of Fe₃O₄ nanoparticles were captured by the GMI effect of Cobased amorphous ribbon sample with excellent magnetic field sensitivity. The results display that the GMI effect of the sample is extremely sensitive for the presence of Fe₃O₄ nanoparticles. While the concentration of Fe₃O₄ is 1 μg/mL, the max GMI ratio（at Hex = 3 Oe） of the sample shows the largest drop, the drop reaches 1.8 %. And, with the increase of the Fe₃O₄ nanoparticles concentration, the drop of the max GMI ratio for the sample becomes smaller at the frequency of 2 MHz. This research indicates that the GMI effect can be widely applied to the detection of weak magnetic sign.