Giant Magnetoimpedance Effect Of Novel Soft Magnetic Composite Materials

With the rapid development of internet of things, high-performance, highly sensitive and fast-response magnetic sensors will be used in automotive electronics, robot technology, bioengineering, automation control, mineral detector, modern military and so on. The sensors can detect or measure magnetic field, speed, rotate speed, displacement, degrees and torque, etc. The giant magneto-impedance (GMI) effect is a novel magnetic sensing technology. Comparing with Hall sensors and giant magnetoresistive sensors, giant magnetoimpedance effect has superior signal intensity and sensitivity at a tiny magnetic field. Comparing with flux gate sensors and Superconducting Quantum Interference Device, the cost of GMI sensors is lower. Comparing with the proton magnetometer and optical pumping magnetometer, the GMI sensor is portable.Experimentally, many soft magnetic materials have exhibited excellent GMI effect, such as Co-based, Fe-based amorphous wires and ribbons, FeNi films and other soft magnetic composite structures. Normally, the diameter of amorphous wires and the thickness of ribbons are up to the micrometer scale, and the multilayer films with a high GMI ratio work in GHz.In theory, GMI effect is normally attributed to a combination of skin effect and high sensitivity of transverse permeability to the external applied field. In a magnetic medium, the skin depth is dependent on the transverse, electrical conductivity and the measuring frequency. Some groups obtained an enhanced GMI value by kinds of annealing methods. But in the film system, skin depth is larger than film’s thinkness. So insulting layers, regulation of peamebility and conductivity were used to enhance GMI ratios of films. In recent years, with the rapid development of nano materials, the size of magnetic sensors is projected to reach the nano-scale. However, traditional GMI materials do not satisfy the desired size, and it is a challenge to find new kinds of nano materials, which can have both an obvious GMI effect and a rapid magnetic response at a low frequency. In this paper, on one hand, we tried to enhance the GMI properties of tranditional mateirals by inducing anistropoy and improving magnetic characters. Several works have been done as follows:1. In this section, firstly, we provided an effective approach for enhancing GMI effect using rapid heat-treatment. The micro-structure of nanocrystalline can be regulated during the rapid heating process. A separation of GMI curve can be observed when submmited a magnetic field, and it can be explained by the anisotropy induced by applied magnetic field in the course of annealing. Secondly, in order to obtain different GMI peak positions, the stripes were ablated by laser with different separations on the top of the ribbon. The peak location drifted to different directions when the stripes were perpendicular or paralleled to the extrernal field. Curvature regulating was also used to enlarge GMI ratio of amorphous ribbons. Meanwhile, the static magnetic properties are similar for the samples before and after the process of laser ablation. Finally, we tried to regulate the GMI ratio by different DC bias current for amorphous ribbons.2. This research is based on the fundamental understanding that transverse permeability plays an important role on GMI effect, therefore a newly developed technique that introducing the coupling effect of nanowires and nano film is developed. On one hand, we regulated the diameters of nanowires by control the size of AAO templates, and changed the compositions of nanowires. The sample combined with50nm Co nanowires and Fe25Ni75film shows the best GMI ratio and sensitivity, which could respectively reach270%and45%/Oe. Besides, the texture of nanowires plays an important role on the GMI effect of nanobrush, which is regulated by controlling the pH and the temperature of deposition process. The optimized GMI effect made by (100) nanowires can reach up to300%. The thinkness of AAO templates was also fabricated to control the GMI ratio of nanobrush. On the other hand, we regulated the GMI properties by changing the thickness of FeNi films and changing the structure of nanobrush. The interlayer of Cu film can regulate the GMI ratio by changing the coupling effect of nanowires and film. At last, Patterned FeCo micrometer pillar with in-plane anisotropy was deposited on the surface of the isotropous FeNi magnetic film of100nm thick by laser-direct-writing via lift-off technology. The optimized MI ratio is more than160%at10MHz, when the micro-pillar with50μn diameter.3. Enhanced magnetoimpedance effect has been observed in carbon-based composite materials. Preprocessed carbon fibers covered by soft magnetic alloys show a good GMI characters. Graphene papers were synthesized in large quantities using a modified chemical approach. Soft magnetic FeNi alloy covered the top and bottom surfaces of graphene paper by electrochemical deposition and magnetron sputtering. Especially, the’stratified FeNi/graphene/FeNi composite exhibited an enhanced magnetoimpedance effect, which is about10times as large as the single-layer FeNi film or multilayer film structure at low frequency.Besides, we made some researches on applications of amorphous ribbons’GMI effect, such as detecting the magnetic field of RMB,3D magnetic field detecting and so on. We also tried to measure transverse permeability of amorphous ribbons using MOKE.