【作者】 沈刚；

【导师】 马学鸣；

【作者基本信息】 上海大学 ， 材料学， 2005， 博士

【摘要】 巨磁阻效应首先在Fe/Cr金属多层膜中被发现,因此对Fe-Cr体系进行深入研究具有现实和理论的意义。Fe-Cr体系虽然在室温下互不固溶,但通过机械合金化的方法可制得纳米晶的固溶体。当Fe-Cr基合金中掺入Mn或V时,其三元合金随温度和浓度的变化呈现出各种有趣的磁现象,但机械合金化制备的三元Fe-Cr-Mn（V）的结构和磁性能尚未见报道。因此,本论文对机械合金化制备的三元Cr-Fe-（V, Mn）合金及其磁性能进行了系统深入的研究。基于铁磁/反铁磁交换偏置在巨磁电阻器件的实用化过程中的重要作用,本论文选择α-Fe为铁磁体,不含Fe且奈尔温度高于室温的反铁磁体作为研究对象,利用穆斯堡尔谱对样品的微结构与铁磁/反铁磁交换相互作用的关系进行了研究。论文简要回顾和总结了机械合金化Fe-Cr体系的微结构和磁性能的的研究历史和现状。概述了交换偏置的基本现象和薄膜体系的交换偏置的研究内容,并对高能球磨铁磁/反铁磁微颗粒的交换偏置的研究进展作了简要介绍。本论文包括的主要研究内容有:采用X-射线衍射和穆斯堡尔效应对两种不同气氛下机械合金化过程中Fe₆₀Cr₄₀粉末的微结构进行了研究。结果表明球磨过程中残留气氛对球磨过程和最终产品具有很重要的作用。Fe₆₀Cr₄₀粉末在球磨罐未抽真空直接充Ar气的条件下球磨,由于残留N2和O2的影响,球磨85h时顺磁性Fe-Cr+N+O结构几乎占100%。而在球磨罐抽真空再充Ar气的条件下机械合金化,得到具有与块体合金大致相同磁性能的纳米晶铁磁性Fe₆₀Cr₄₀无序固溶体。采用X-射线衍射、穆斯堡尔效应和磁性能测量研究了机械合金化过程中Fe_xCr_90-xV₁₀（x=18, 35）粉末的微结构和磁性能变化。并结合对磁滞回线的计算机拟合分析,建立了机械合金化制备的纳米晶Fe_xCr_90-xV₁₀（x=18, 35）合金的微结构模型。研究结果表明, Fe_xCr_90-xV₁₀（x=18, 35）粉末在球磨过程中,由于单质V相的较快消失,Fe原子组态由α-Fe、富Fe的铁磁性Fe（Cr, V）相和富Cr的顺磁性Cr（Fe, V）相组成。α-Fe组元随球磨时间增加单调减少,富Fe的Fe（Cr, V）相随球磨时间延长先增加后减少,顺磁相随球磨时间的增加而单调增加。球磨50h,形成了bcc结构的顺磁性纳米晶Cr-Fe-V合金。在富Cr的合金成份内,Fe含量越高,生成均质的纳米晶Fe-Cr-V合金所需的球磨时间越长。随着球磨时间的增加,样品室温磁滞回线的高场部分不饱和性越强,比饱和磁化强度单调减小,矫顽力和剩磁比在球磨初期显著增加,而后趋于饱和。Fe含量越高,相同球磨时间样品的矫顽力和剩磁比越小。Fe_xCr_90-xV₁₀（x=18, 35）粉末在不同球磨时间存在超顺磁驰豫更多还原

【Abstract】 Since the giant magnetoresistance （GMR） effect was first discovered in Fe/Cr multilayers, the intensive study on the Fe/Cr systems has possessed theoretical and practical significance. Though Fe and Cr are immiscible at room temperature, nanocrystalline solid solution can be prepared by mechanical alloying （MA）. When Mn or V is doped into Fe-Cr alloys, the ternary alloys exhibit many interesting magnetic properties as a consequence of the variation in composition and temperature, however, the structural and magnetic properties of the ternary Fe-Cr-Mn（V） alloys prepared by mechanical alloying have not been reported yet. Consequently, the structural and magnetic properties of the MA ternary Fe-Cr-Mn（V） alloys had been intensively investigated on this thesis. For the important role of ferromagnetic/ antiferromagnetic interactions on the practice of the GMR equipments,α-Fe was chosen as the ferromagnetic material and the materials whose Néel temperatures are above room temperature and elemental composition is free of Fe as the antiferromagnetic one, and the relationship between the microstructures indicated by M?ssbauer spectroscopy and the ferro-antiferromagnetic interactions had been investigated on the thesis.The history and present status about the structural and magnetic properties of MA Fe-Cr systems have been briefly reviewed and summarized on the thesis. The basic phenomena of exchange bias and the exchange bias in thin film were summarized, and the development of the exchange bias in high-energy ball milled ferro-antiferromagnetic powders was also briefly introduced. The main contents are as follows:The structural properties of mechanically alloyed Fe₆₀Cr₄₀ powders under two different atmosphere were investigated by X-ray diffraction （XRD） and M?ssbauer spectroscopy. The results show that the residual N₂ and O₂ in the mill vials have drastically effect on the structures of the final milling products. When the vials are full of Ar without vacuumize, the paramagnetic Fe-Cr+N+O structure almost represent 100% of the final product after powders milled for 85h. When the vials are full of Ar with previous vacuumize, the final milling product is disorder nanocrystalline Fe-Cr solid solution with ferromagnetism similar to the bulk alloys.The structural and magnetic properties of MA Fe_xCr_90-xV₁₀（x=18,35） were investigated by XRD, M?ssbauer spectroscopy and magnetic measurements. A simple更多还原