【作者】 宋远强；

【导师】 张怀武；

【作者基本信息】 电子科技大学 ， 材料物理与化学， 2009， 博士

【摘要】 稀磁半导体（DMS）是实现自旋电子器件的材料基础。借助这种材料可以实现电子自旋的控制、输运和注入。尤其是最近发现的具有室温铁磁性的稀磁性氧化物体系，借助这种材料可以实现室温下的自旋过滤作用，使自旋电子器件的实用化成为可能，该方向也成为自旋电子学领域的研究热点。本文首先从材料设计理论入手，选择多种过渡族元素（V，Cr，Mn，Fe，Co，Ni）掺杂的宽禁带氧化物CeO₂体系为研究对象，使用WIEN2k软件包采用先进的LDA+U方法，通过对体系电子结构和态密度的计算，预测具有铁磁性的掺杂体系，并从理论上分析其铁磁性交换机制和起源问题，主要是氧空位对掺杂磁性离子耦合机制的影响及对体系铁磁性产生的贡献，首次从理论上发现：在掺杂CeO₂体系中磁性离子是通过氧空位产生的铁磁性耦合，符合氧空位诱导铁磁性交换耦合机制。在此理论的指导下，实验上采用平衡（固相烧结）和非平衡（磁控溅射，脉冲激光沉积-PLD）方法制备不同掺杂体系、不同浓度和共掺杂的CeO₂基稀磁氧化物薄膜和块材。制备过程中通过改变工艺条件、后处理退火等手段，对样品进行磁性能测试、微结构表征，辅助XPS和Raman光谱测试来研究对材料的室温铁磁性的影响。最终得到具有室温铁磁性的Ce_0．97Co_0．03O_2-δ块材和薄膜样品，其居里温度分别高达625K和760K。其室温铁磁性与氧空位浓度的关系在氧空位诱导铁磁性耦合机制下可以得到完美的解释，并通过共掺杂实验和Ar⁺轰击方法对氧空位诱导铁磁性耦合机制进行了进一步实验验证。最后，采用四靶磁控溅射系统制备了具有不同中间层厚度的Ni（80nm）/Ce_0．97Co_0．03O_2-δ（d nm）/Co₅₀Fe₅₀（80nm）三层膜结构单元（d=1nm，3nm，5nm，10nm），并通过磁阻（MR）测试在d=5nm的样品中得到室温下5％的磁电阻，从而证明了Ce_0．97Co_0．03O_2-δ材料的室温自旋过滤功能，展现出CeO₂基稀磁氧化物材料在自旋相关器件中巨大的应用前景。更多还原

【Abstract】 Diluted magnetic semiconductor （DMS） is a key material for spintronics andrelated devices.Via this type of functional materials,the spins of electrons can beutilized,as the spin transportation and spin injection would be realized.Especially therecently developed diluted magnetic oxide,its high curier temperature （T_C） which iswell above room temperature,via which spin filtering-effect can be realized at roomtemperature,fundamentally facilitate the progress of spintronic-related devices onpractical aspect,and thus this field is being paid more and more attentions.Firstly,based on first principle calculations,several transitional elements （such as V,Cr,Mn,Fe,Co,Ni） doped CeO₂ systems are investigated with LDA+U methods in WIEN2kpackage.By calculating the electronic structure and density of state,the doped systemswith ferromagnetism （FM） are predicted,and the exchange coupling mechanism amongthe doped magnetic ions are further investigated,mainly focusing on the oxygenvacancy （V_O） related ferromagnetic exchange coupling mechanism.It is found thatmagnetic ions forms ferromagnetic coupling via Vo,which is well consistent withVo-induced ferromagnetic exchange coupling mechanism.And then from experimentalaspects,doped CeO₂ bulk and thin films with different elements and varied dopingcontents are synthesized by equilibrium methods （including solid-state reaction） andnon-equilibrium methods （including magnetron sputtering,pulsed laser deposition-PLD,and E-beam evaporation）.With varied technology parameters and adopted postannealing,magnetic properties,micro-morphologies,as well as X-ray photoelectronspectroscopy （XPS） and Raman spctra of different samples are measured,to investigatethe influential factors for room temperature （RT）- FM.It is found experimentally thatthe FM is best for samples with the stoichiometry of Ce_0.97Co_0.03O_2-δ,with a highestCurier temperature of 625K and 760K for its bulk and thin films,respectively.The V_Orelated FM can be well explained by Vo-induced ferromagnetic coupling mechanism,and further experiments of co-doping and Ar⁺-bombardment methods are carried out forfurther investigation.At last,a three layered- structure of Ni（80nm）/Ce_0.97Co_0.03O_2-δ（dnm）/Co₅₀Fe₅₀（80nm） with viaried thickness of the inter layer （d=1,3,5,10 nm, respectively） are fabricated via four-targes magnetron sputtering system.Magneticresistance measurements indicate a 5% MR value in the sample with d=5nm thickness.This results provide a provement of the RT-spin filtering effect of Ce_0.97Co_0.03O_2-δ thinfilms,exhibiting a wide potential applications in spin-related devices.更多还原