【作者】 张可；

【导师】 姚斌；

【作者基本信息】 吉林大学 ， 凝聚态物理， 2007， 博士

【摘要】 本论文系统研究了Fe (Co)-Zr-B-Nb(FZBN)软磁非晶合金体系的热稳定性、非晶形成能力(GFA)和磁性能随合金元素变化的规律及相互关系,总结出B含量对非晶FZBN晶化模式、晶化产物和磁性能的影响规律,发现了FZBN非晶的GFA、热稳定性和软磁性能随B含量的变化规律和机制;阐明了FZBN非晶的表象激活能(Eg)意义及与晶化和玻璃转变温度(Tx和Tg)的关系: ;给出FZNB非晶的GFA(用过冷液相区△　Tx表示)与E_g和T_g关系:系统研究了Fe基和Co基合金的磁阻抗(MI)效应,在淬态FZBN合金中观察到显著的MI效应,在1.1 MHz时最大的MI比值达到180%;在低频(小于1 MHz)条件下,首次在Fe基纳米晶条带中获得磁阻抗比值超过700%、磁场灵敏度高达108%/Oe的MI效应;在Co基合金条带中发现了MI效应随退火温度变化的新规律。更多还原

【Abstract】 Fe- and Co-based metallic glasses and nanocrystalline alloys as good magnetic materials, which have important application in power transportation, computer storage and read-write magnetic apparatus, have great economic benefit and wide application prospect. In these years, they have become one of the important research subjects.Fe91-xZr5BxNb4 (FZBN) nanocrystalline alloy system with low B content (x≤20) has been extensively studied because of its excellent soft magnetic properties and very interesting magnetic exchange interaction in amorphous state. However, the mechanism for the influence of B content on the glass forming ability (GFA), thermal stability, magnetic properties and exchange interaction is not yet clear in high B content above 20 at.% for Fe-based amorphous alloys, and is still argumentative. It is helpful to understand magnetic exchange interaction of Fe atomic couples in the Fe-rich amorphous alloy and prepare bulk glasses by investigation of effect of substitution of B for Fe on the glass forming ability, crystallization and magnetic properties in wider B content range. So we prepared Fe91-xZr5BxNb4 (FZBN) alloys and investigated the effects of B content on crystallization, glass forming ability and magnetic properties. It is found that GFA reaches maximum near eutectic composition of x=27.5. FZBN amorphous alloys crystallized in primary crystallization mode at low B content range of x≤20, but in eutectic mode at high B range of 20<x<30 and in polymorphous mode at x=30. A metastable Fe-Zr-B-Nb cubic phase with saturated magnetization of 137 emu/g and coercivity of 7.3 Oe at room temperature forms in polymorphous crystallization process. The glass transition temperature (Tg), crystallization temperature (Tx), Curie temperature (Tc) and magnetization (Ms) of the FZBN amorphous alloys increase with increasing B content, while its coercivity (Hc) decreases. When the B content exceeds 20, not only the Tg, Tx and GFA increases sharply, due to the change of crystallization mode, but also the B content dependences of Tc,Ms and Hc change. The FZBN amorphous alloys with x = 25 to 30 exhibit better GFA, thermal stability and soft magnetic properties.In addition, apparent activation energies (Eg) of glass transition, glass transition temperature (Tg) and crystallization temperature (Tx) of amorphous alloys of composition Fe91-xBxZr5Nb4 (FBZN, 5≤x≤30 at. %) and Fe61-xCoxZr5B30Nb4 (FCZBN, 0≤x≤15 at. %) were obtained by using differential scanning calorimeter (DSC) measurement and Kissinger equation, and correlations between Eg and Tg, Tx and glass-forming ability (GFA) were studied in the present work. It was found that the Tg and Tx are not independent each other for each glass composition in the two alloy systems, but related by a formula, Tx=αTg+β, whereαandβare constants, and were measured by nonisothermally scanning in the DSC together with the Lasocka’s equation. The Eg was found to be directly proportional toαandβ, respectively, and had a correlation with Tx and Tg, indicating that Eg determines linear relationship between Tx and Tg.. Supercooled liquid region ?Tx is used as characterization of GFA of the Fe based metallic glasses and related to Eg and Tg by a formula: indicating that Eg and Tg can characterize GFA of the Fe based metallic glass well.Another important use of Fe- and Co-based soft magnetic alloys is the application as magnetoimpedance materials. In 1992, Mohri et al. firstly reported that when an alternative current flows through a CoFeSiB wire, the ac voltage between the two ends of the wire would change sensitively with an applied magnetic field along the wire, and named the phenomenon the giant magnetoimpedance (GMI) effect. Initially, researches on the phenomenon were focused on Co-based soft magnetic amorphous wires with zero or negative magnetostriction. With the development of further investigation, Fe-based nanocrystalline soft magnetic alloys——the new type of nano soft magnetic material, were developd. As Fe-based nanocrystalline soft magnetic alloys possess very good soft magnetic properties and are one of the best MI materials, they have been paid great attention all over the world. Moreover, considering the shape and structure of materials, the researches of MI effect have extended to films, sandwiched structures and amorphous wires with multiple structures. As the MI effect occurs at room temperature and commonly shows high sensitivity at low applied magnetic field, it has potential application in all sorts of magnetic sensors, magnetic sensitivity switch and automatization control system.Now it has been widely accepted that the main characteristics of MI effect can be understood in the frame of classical electrodynamics. The applied magnetic field and driving current change the impedance of material through influencing permeability and skin depth, and thus induce MI effect. Recently, a lot of studies on the MI effect have been carried out. It has been found that the MI effect is affected by many factors, such as magnetostriction, domain structure, magnetic anisotropy and so on. However, some problems still exist due to the difference of preparation and treatment techniques and complex magnetization mechanisms.According to the current status of the studies on the MI effect and our experimental conditions, we prepared Fe- and Co-based ribbons, performed proper thermal treatments on them and investigated the MI effect at different frequencies in the ribbons under room temperature. Following are summaries of our works:1. A systematic investigation of the influence of B content on the MI effect in melt-spun Fe91-xZr5BxNb4 (FZBN) (x=0-30) ribbons has been performed. A distinct MI effect has been observed in melt-spun Fe-based ribbons for the first time. The large MI effect is obtained with a maximum change of 180% at around 1.1 MHz in the sample with x=20, and a field sensitivity of about 7%/Oe. The significant MI effect is attributed to a domain structure formed by the inhomogeneous stress induced during the quenching process. Due to this domain structures, the FZBN amorphous alloy with x = 20 may possess a high permeability and nealy zero magnetostriction. This results in the large MI effect. 2. The impact of thermal treatment on the microstructure, magnetic properties and MI effect of Fe84.5Zr4B8.5Nb2Cu1 (FZBNC) ribbons has been studied. When the annealing time keeps for 20 min, it is found that the mean grain size of the nanocrystalline phase and soft magnetic properties of FZBNC change greatly with the increasing annealing temperature. When the annealing temperature is higher than 495℃, the MI behavior changes from single-peak curve two-peak curve, and the maximum MI ratio is enhanced greatly. A large MI ratio more than 700% at frequency lower than 1 MHz is observed in Fe-based ribbons. The FZBNC ribbon annealed at 575℃exhibits the most drastic MI ratio of 756% at 600 kHz accompanied by the field sensitivity of 108%/Oe. The significant MI effect in FZBNC annealed at 575℃is attributed to the excellent soft magnetic properties, which are due to the proper grain size of theα-Fe phase and the higher Curie temperature of the intergranular amorphous phase.3. The impact of annealing time on the MI effect in FZBNC alloys has been investigated. It is found that coercivity and resistivity for FZBNC annealed at 575℃for 60 min decrease to some extent compared with the sample annealed for 20 min. The MI curves of FZBNC annealed for 60 min show two-peak behavior and the maximum MI ratio at any measuring frequency is higher than that of the sample annealed for 20 min, especially reaches 768% at 600 kHz. However, as the grain size for the sample annealed for 60 min increases greatly, the ribbon becomes fragile and is not propitious to use.4. The MI effect in Co72-xFexZr8B20 (CFZB,x=0,2,5,7at.%) amorphous alloys has been studied. A large MI effect has been observed in the as-quenched Co-based ribbons. The sample with 0 at.% Fe content doesn’t possess the smallest coercive force and near zero magnetostriction, but it shows the most prominent MI value of 90% at 1110 kHz and the largest field sensitivity of 18%/Oe. Analysis on the effect conclusively demonstrates that high permeability determined by the domain structure of the material, large change of permeability with applied magnetic field and smaller electrical resistivity play the dominant roles in this MI effect.5. Vacuum heat treatment was performed on the Co72Zr8B20 ribbons. It is found that with the increasing annealing temperature, the soft magnetic properties of Co72Zr8B20 gradually deteriorate due to the change of microstructure, which leads to the reduction in the MI effect. Moreover, the MI curves for the sample in the as-quenched state and annealed at 495℃show single-peak behavior. After the sample being annealed at 540℃, double-peak MI curve is observed, which is attributed to induced transverse magnetic anisotropy. Although small transverse anisotropy generally contributes to optimized MI behavior, large MI value isn’t obtained in the annealed sample as the soft magnetic properties play the dominant role in the MI effect.更多还原