【作者】 郭红；

【导师】 晁月盛；

【作者基本信息】 东北大学 ， 材料物理与化学， 2010， 博士

【摘要】 巨磁阻抗(简称GMI)效应器件,因在室温、低外磁场下具有大的、高灵敏度交流阻抗改变等特点,使其在传感技术领域中具有巨大的应用前景。非晶纳米晶材料在较低交变驱动电流频率下可获得显著巨磁阻抗效应,因而倍受关注。本论文采用低频脉冲磁场处理工艺,制备了Fe78Si9B13、Co68.15Fe4.35Si12.5B15和Fe73.5Cu1Nb3Si13.5B9非晶纳米晶双相合金。采用穆斯堡尔谱(Mossbauer)、透射电子显微镜(TEM)和X射线衍射仪(XRD)等手段对低频脉冲磁场处理前后样品Fe78Si9B13的微结构进行分析；利用自制巨磁阻抗测量仪测量低频脉冲磁场处理前后Fe78Si9B13、 C068.15Fe4.35Si12.5B15和Fe73.5Cu1Nb3Si13.5B9样品的巨磁阻抗,分析探索低频脉冲磁场处理参数、直流外磁场及交变驱动电流频率对非晶合金样品巨磁阻抗效应的影响规律；利用交变梯度磁强计测量低频脉冲磁场处理前后Fe73.5Cu1Nb3Si13.5B9非晶纳米晶样品的磁滞回线和磁化曲线,并由此计算样品的矫顽力Hc、饱和磁化强度Ms和起始磁导率μi；采用改进的杨氏模量仪对低频脉冲磁场处理前后Fe73.5Cu1Nb3Si13.5B9非晶纳米晶样品的饱和磁致伸缩系数λs进行测量,研究低频脉冲磁场处理工艺对样品软磁性的优化；以相变热力学和相变动力学理论为基础,探讨了低频脉冲磁场致非晶合金纳米晶化的机理；在经典电磁理论框架下,解释材料巨磁阻抗效应的产生机制,并利用微分算子消元法求解Maxwell微分方程组,得到非晶纳米晶薄带横向磁导率通式。论文主要结论归纳如下：低频脉冲磁场处理可致非晶Fe78Si9B13合金发生低温初始纳米晶化,处理过程样品温升△T<7℃,作用时间不超过5分钟。低频脉冲磁场制备非晶纳米晶方法,克服了传统等温退火处理和电脉冲处理等方法存在的工艺周期长、处理过程样品温升大的弊端,提出了一种低温下非晶合金纳米晶化的新工艺。低频脉冲磁场处理Fe78SigB13非晶合金,在合金内产生的磁致伸缩效应,为非晶合金相转变提供了激活动力,降低了形核势垒,最终在非晶Fe78Si9B13基体上析出8nm左右的α-Fe(Si)晶粒。析出纳米晶的晶化相体积分数与脉冲磁场处理参数有关,当脉冲磁场强度Hp为2500e,脉冲频率f为30Hz,脉冲作用时间t为4min参数下,样品晶化相体积分数最大。非晶纳米晶样品的矫顽力总体较其制备态非晶合金样品有所降低,饱和磁化强度Ms有提高趋势,非晶纳米晶样品的饱和磁致伸缩系数λs低于制备态非晶合金,这表明低频脉冲磁场处理优化了非晶合金的综合软磁性能。低频脉冲磁场处理后C068.15Fe4.35Si12.5B15非晶纳米晶样品的磁阻抗发生明显变化,脉冲磁场参数不同,制备所得样品的GMI效应大小不同。实验表明,在脉冲强度Hp为350kAm"1、脉冲频率f为25Hz、脉冲作用时间t为4分钟条件下制备的Co68.15Fe4.35Si12.5B15非晶纳米晶样品GMI效应最为显著,GMI效应值高达263.5%。低频脉冲磁场处理给出了一种全新的、获得较高GMI效应的材料处理工艺。低频脉冲磁场处理致非晶合金纳米晶化时,在样品内产生感生各向异性。感生各向异性提高了样品的GMI效应及其灵敏度。实验显示,当直流外磁场Hex等于样品内横向磁各向异性场Hk时,非晶纳米晶样品的GMI出现峰值。GMI效应与样品的元素组分有关,Co68.15Fe4.35Si12.5B15样品的GMI效应及其灵敏度大于Fe73.5Cu1Nb3Si13.5B9,而其GMI的效应特征频率ωm却低于Fe73.5Cu1Nb3Si13.5B9; GMI效应存在尺寸效应,在磁脉冲参数相同条件下,相同材料厚度不同、宽度不同,样品的GMI效应不同,厚度大、宽度窄的样品GMI效应较大。GMI效应是交变驱动电流频率ω的函数,非晶纳米晶样品存在一特征频率ωm,当交变驱动电流频率ω=ωm时,样品的GMI效应出现峰值。样品的特征频率与非晶纳米晶的制备历史有关,非晶纳米晶样品的特征频率ωm总体低于制备态非晶合金。采用微分算子消元法解Maxwell微分方程组,得到GMI效应下非晶纳米晶薄带横向磁导率μeff通式,并结合不同交变驱动电流频率段下的磁化机制,解Landau-Lifshitz方程,求出纳米晶薄带横向磁导率ueff的具体表达式。计算结果表明,交流磁化下非晶纳米晶薄带磁导率与直流外磁场Hex、交变驱动电流频率ω及材料的磁性参数大小有关,同时具有取向相关性。更多还原

【Abstract】 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.更多还原