Investigation Of Giant Magneto-impedance Effect In CoP/Insulator/BeCu Microwire Resonator

CoP/Insulator/BeCu composite wires have been prepared by electroless deposition. Because of the polyester between CoP layer and BeCu core,a capacitance is formed. By changing the connecting methed of composite wire during measuring,a resonator is constructed and the GMI effect in it can be improved greatly.The expression of impedance and phase of the composite wire is deduced in theory,and also,many aspects of the sample such as GMI ratio,field sensitivity,frequency characteristics have been studied on experiment.Through changing the geometry,aftertreatment and measuring methods,gaint magneto-reasonace impedance ratio have been invatigated.The main content and results are as follows:1.CoP soft magnetic alloy was deposited on polyster-coated BeCu wires by electroless deposition.Unlike the traditional measurment,a resonator appeared due to using different way.The impedance is the total of whole circuit,which is related to not only magnetic properties of ferromagnetic material but also the capacitance and measurement circuit.GMI ratios change suddenly nearby resonance frequency, and then decrease obviously when frequencies keeping away from them,showing distinct selectivity of frequency.2.The phase and impedance curves were simulated using an equivalent circuit and the calculated values agreed well with the experimental data,which means that both of the equivalent circuit and the parameters of capacitances and inductance are reasonable.At low frequencies,the equivalent circuit can be seemed as a normal measurment circuit,as the frequencies go higher,the whole circuit is similar to a reasonance circuit.Because of reasonances,the impedance change 216.93 5Ωat 60MHz and GMI ratio goes up to 793.1%at 79.6MHz which is much higer than traditional sample's 69.7%at the same frequency.The maximal field sensitivity is 32.7%/Oe,about 9 times bigger than traditional sample's sensitivity at this frequency.3.Investigated the influences of length of the composite wire,electric annealing current density,driving current on resonance frequency.They all can change the value of local resistance and indyctance.Resonance frequency transformed regularity.As the length change from 6cm,8cm to 10cm,resonance frequences become lower and lower.GMI ratio increase at first and then decrease when the DC jouble annealing current decsity increase.GMI effect get maximum at 1.895×10~8 A/m~2.The effect of driving current on GMI is investigeted too,the magnetization process of ferromagnetic material is influenced by magnitude of driving current.As a result,the GMI effect is influenced.The result show that GMI ratio and reasonance frequences at higher frequences change hardly,But,at lower frequences,GMI ratio changes as the same as the driving current magnitude.4.Many more compound samples' GMI ratio and resonance frequency characteristics have been investigated,and this is why the equivalent circuits are more complicated,and some new phenomenon have arisen,for example when a LC resonance sample connects a traditional sample,because of bringing in inductance,reasonance frequency get down.