Giant Magneto Impedance Effect Of Fe-based Amorphous Nano-crystallization Caused By Low Frequency Pulsation Magnetic Field

Giant magneto impedance effect (GMI) memory element, which has high magneto impedance effect and sensitivity under room temperature and low external magnetic field, bears enormous application prospects. Much and wide attention is now paid to amorphous nano-crystal material because it can gain remarkable GMI effect under low drive current.The paper illustrates the method to prepare amorphous nano-crystal double-phase alloy, i.e., processing amorphous alloy Fe78Si9B13. C068.15Fe4.35Si12.5B15and Fe73.5Cu1Nb3Si13.5B9in low frequency pulsating magnetic field.adopting such methods as Adopting methods such as Mossbauer spectroscopy, TEM and XRD to analyze the change of the sample’s microstructure before and after the processing; On the other hand,adopting self-made GMI meter to test the nano-crystal GMI of amorphous sample Co68.15Fe4.35Si12.5B15and Fe73.5Cu1Nb3Si13.5B9before and after the processing in low frequency pulsating magnetic field to explore the law、influence of low frequency pulsating magnetic field processing parameter and drive current frequency on nano-crystal alloy’s GMI; calculating the coercive force Hc, saturation magnetization Ms by adopting alternating gradient magnetometer to test the magnetic hysteretic loss and magnetize curve of sample Fe73.5Cu1Nb3Si13.5B9before and after the processing in pulsating magnetic field.studying the optimization effect of low frequency pulsating magnetic field processing technique on magnetic property of the sample’s material by adopting improved Young’s modulus to measure the nano-alloy saturation magnetostriction coefficient λs of sample Fe73.5Cu1Nb3Si13.5B9, exploring the mechanism of amorphous alloy nano-crystallization caused by low frequency pulsating magnetic field based on phase change thermodynamics and phase change dynamics; in the frame of classical magnetic theory, explaining the mechanism of material’s GMI effect and calculating the traverse magnetic permeability general formula by amorphous alloy ribbons under different frequency bands. Main conclusions are as follows:Low frequency pulsating magnetic field processing amorphous alloy Fe78Si9B13causes initially nano-crystallizing. The temperature of the sample rises less than7℃and the processing time of is not more than5minutes. The way that using low frequency pulsating to prepare nano-crystal overcomes the disadvantage of traditional ways such as isothermal anneal and electric pulsing anneal, the technique period of which is long and temperature rise in the process is high. A new method of amorphous nano-crystallization under low temperature is invented.Magnetostriction effect developed in alloy by processing amorphous alloy Fe78Si9B13provides amorphous alloy phase change with activation power and lower nucleation potential barrier, as a result, separating out α-Fe (Si) crystal grains around8nm. The volume fraction of crystallization phase changes in a non-monotonic way with magnetic pulse parameter. When the intensity of magnetic pulsing field is at250Oe, the frequency is30Hz and the time is240s, crystal phase volume fraction attains maximum.The coercive force Hc, saturation magnetostriction coefficient λ, decreases wholly compared with those of prepared configuration amorphous alloy, which means that magnetic pulse processing optimizes the soft magnetism of amorphous alloy.The magnetic impedance of amorphous nano-crystal sample C068.15Fe4.35Si12.5B15obviously changes by low-frequency magnetic pulsing field preparing, the magnetic impedance of amorphous nano-crystal value will be different under different low frequency pulsing magnetic field parameter. Study shows that the best parameter is magnetic pulse intensity Hp=350kAm-1, magnetic frequency f=25Hz, processing time t=4min. The amorphous nano-crystal sample Co68.15Fe4.35Si12.5B15made under such parameter can produce GMI effect activity and reach maximum GMI value of263.5%. The method of low frequency pulsating magnetic field provides us a new material processing technique to acquire high GMI effect.Induced anisotropy generates during the process of amorphous alloy nano-crystallization caused by low frequency pulsating magnetic field. Induced anisotropy enhanced GMI value and sensitivity of sample. Study shows that when Hex equals to the transverse magnetic anisotropy Hk, GMI of sample reaches peak value.On the other hand, GMI effect of sample has relation with material’s element composition, the GMI value and the sensitivity of C068.15Fe4.35Si12.5B15is much higher than those of Fe73.5Cu1Nb3Si13.5B9; while the characteristic frequency of C068.15Fe4.35Si12.5B15is lower than that of Fe73.5Cu1Nb3Si13.5B9; size effect of GMI on sample was then studied, testing GMI of a material with different thickness and width under the same preparation condition and parameters, results show that increasing thickness of material (or increasing conductivity) can make GMI effect move toward low frequency; GMI of narrow-band sample is higher than that of broad-band one.GMI effect of sample is the function of AC current drive frequencyω, sample brought out different GMI effect under different drive current frequency, when characteristic frequency ωm of amorphous nano-crystal equals to drive current frequency ω, GMI of sample reaches the peak value. Results show that ωm is related to the history of preparation,ωm of amorphous nano-crystal is lower than that of prepared configuration amorphous alloy.Adopting differential operator elimination element to solve system of differential equations to get the general formula of magnetic ribbon transverse magnetic permeability μeff, combining with magnetization mechanism under different frequency to solve the equation of Landau-Lifshitz get tensor magnetic susceptibility substituting the general formula of transverse magnetic permeability to work out specific expression of transverse magnetic permeability μeff of low, medium and high frequency band. The result shows that ribbon magnetic permeability under AC magnetization is related to the intensity of external magnetic field Hex、drive current frequency ω and magnetic parameters of material, simultaneously bears tropism correlation.