【作者】 刘晖；

【导师】 姜恩永； 白海力；

【作者基本信息】 天津大学 ， 材料物理与化学， 2004， 博士

【摘要】 金属—绝缘体颗粒薄膜系统中存在的隧穿型磁电阻效应、巨霍耳效应、高矫顽力效应等新特性,使其在磁性传感器件、高密度记录介质、读出磁头以及磁性随机存取存储器等技术领域具有广阔的应用前景。研究金属颗粒系统中纳米结构引起的新现象,解明巨霍耳效应的机理,探索巨霍耳效应在技术领域应用的可能性,以及制备室温条件下具有较大磁电阻效应的颗粒薄膜是目前凝聚态物理和材料科学研究领域的热点问题。本论文采用磁控溅射法制备了Cu-SiO2、Zn-SiO2、NiFe-SiO2、Fe-Ge、Fe3O4-SiO2等不同体系的金属—绝缘体颗粒薄膜,对它们的微观结构、化学成份、电阻率、磁电阻、霍耳电阻、磁性能等进行了系统研究。首次在Cu-SiO2非磁性金属—绝缘体颗粒薄膜体系中发现了巨霍耳效应,提出了非磁性金属颗粒系统巨霍耳效应的局域量子干涉理论模型,并定量地解释了Cu-SiO2系统的巨霍耳效应。通过对Cu-SiO2退火样品以及Zn-SiO2颗粒薄膜霍耳效应的研究,又从实验上进一步验证了该理论模型之正确性。通过对NiFe-SiO2中正常和反常霍耳效应的对比研究,首次发现颗粒膜系统的特殊逾渗结构对巨霍耳效应的形成所起到的关键作用,为解明磁性金属颗粒膜系统中的巨霍耳效应提供了新的思路。首次在Fe-Ge 颗粒薄膜中发现了霍耳电阻的巨大增强效应,其霍耳灵敏度比目前应用的硅半导体霍耳传感器件高出一倍以上。样品的基本技术参数满足霍耳传感器的要求,为巨霍耳效应在技术领域的广泛应用提供了基础实验数据。在室温条件下制备了Fe3O4半金属颗粒薄膜,在目前已报道的多晶Fe3O4薄膜材料中具有较大的室温磁电阻值。首次发现并证明了多晶Fe3O4薄膜中存在反铁磁耦合现象。研究了SiO2对Fe3O4薄膜输运性能的影响。在满足TMR器件制备要求的前提下(温度低于573 K、厚度小于50 nm),Fe3O4薄膜的磁电阻仍保持在-5.4%以上,阐明了Fe3O4颗粒薄膜在TMR器件上的应用的可能性。更多还原

【Abstract】 Excellent properties such as tunneling magnetoresistance (TMR), giant Hall effect (GHE), huge coercivity have made metal-insulator granular films promising candidates for the application of magnetic sensors, high density magnetic recording materials, read-out magnetic head and magnetic random access memory. Researching of new properties in these nano-structures, uncovering the mechanism of GHE, exploring the probability of GHE for practical usage, and fabrication of films with high MR at room temperature has becomes one focus in the field of condensed matter physics. This is also the aim and major work in this thesis. Different types of metal-insulator films were prepared by using magnetron sputtering, including Cu-SiO2, Zn-SiO2, NiFe-SiO2, Fe-Ge and Fe3O4-SiO2 systems. Properties such as structure, composition, resistivity, magneto-resistivity, Hall effect and magnetic properties of systems mentioned above have been carefully studied. For the first time, we find GHE in non-magnetic metal-insulator granular system, i.e. Cu-SiO2 mixture. The theory base on local quantum interference effect was proposed and has been successfully applied in Cu-SiO2 system. Through the research of Hall effect in Cu-SiO2 annealing samples and Zn-SiO2 granular system, this model has been testified. The important effect of percolating structure to GHE has been found for the first time in the comparing study on both ordinary and extraordinary Hall effect of NiFe-SiO2 system. This provides a relatively new method for understanding the mechanism in GHE. Giant enhancement of Hall resistance was firstly observed in Fe-Ge granular film and its Hall sensitivity is above one time larger that of Hall sensors which based on Si used today. This provides it a promising application for GHE. Fe3O4 films with the largest MR reported till now have been prepared at room temperature. For the fist time, anti-ferromagnetic coupling effect was found in polycrystalline Fe3O4 films. Effect of SiO2 on transport properties of Fe3O4 films was also studied. Fe3O4 film which fulfills the requirement of TMR sensors still has high MR ratio of above -5.4%, and this makes it possible for the Fe3O4 used as TMR elements.更多还原