钙钛矿镍酸盐异质结构的制备与性能研究
发布时间：2018-07-26 15:23
【摘要】：近些年来,以镍酸盐为代表的钙钛矿关联氧化物材料一直是凝聚态物理和材料科学研究的热点。在钙钛矿镍酸盐异质结构中,晶格、电荷、自旋和轨道自由度之间强烈的相互作用使得该类材料有着复杂的物理性质。通过应变、尺寸、超晶格结构设计等手段调控这些自由度,可以实现对材料的电、磁特性的调控。本论文以镍酸盐异质结构为研究对象,制备了 LaNiO_3(LNO)超薄膜和LaNiO_3/LaMnO_3(LNO/LMO)超晶格结构,研究了其电、磁特性,并通过应变、尺寸效应、缓冲层的插入以及超晶格结构的设计等手段对其输运特性、磁性进行了调控,具体工作如下:(1)利用脉冲激光沉积技术(PLD)和反射高能电子衍射仪(RHEED)在(001)方向的SrTiO_3(STO)和LaAlO_3(LAO)单晶衬底上分别外延生长了一系列不同厚度的LNO超薄膜。X射线衍射(XRD)表征表明STO衬底上的LNO薄膜受拉应力作用。原子力显微镜(AFM)表征表明超薄膜具有原子级别平整的表面。输运特性测试表明,随着薄膜厚度的减小,薄膜电阻逐渐增大。当厚度小于某一临界值时,LNO由金属态变为绝缘态。在STO和LAO衬底上这一临界厚度分别为5和4个晶胞(u.c.)。对面电阻-温度曲线的拟合结果表明该转变的起因是LNO薄膜中载流子的局域化效应。(2)在5u.c.厚的LNO薄膜与STO衬底间插2u.c.厚的STO薄膜作为缓冲层后,LNO薄膜的输运特性发生了明显的变化,温度高于100 K时LNO由绝缘态变为金属态。X射线光电子能谱仪(XPS)分析表明低氧压下(10-3mbar)生长的STO薄膜中存在氧空位。LNO薄膜输运特性的变化可归因于STO薄膜中的氧空位。氧空位提供了大量电子,电子从STO层转移到LNO层,抑制了LNO层中载流子的局域化。通过对STO薄膜进行退火处理以及提高生长氧压,STO薄膜中的氧空位大大减少,5u.c.厚的LNO薄膜又恢复了绝缘态。(3)利用PLD在(111)方向的STO单晶衬底上生长了[(LNO)m/(LMO)n]x超晶格薄膜。磁性测试结果表明在低温下这一包含顺磁铁磁界面的体系中存在交换偏置现象,其原因可能是界面处电荷转移导致的铁磁相互作用。改变超晶格周期数x和LNO组元的层数m后,超晶格的交换偏置场HE和矫顽场HC的大小均发生了变化,具体表现为:随着周期数x和LNO组元的层数m的减小,交换偏置场HE和矫顽场HC均变小。
[Abstract]:In recent years, perovskite-related oxide materials, represented by nickel, have been a hot topic in condensed matter physics and material science. In perovskite nickel heterostructure, the strong interaction between lattice, charge, spin and orbital degree of freedom makes the material have complex physical properties. These degrees of freedom can be regulated by means of strain, size and superlattice structure design, which can control the electrical and magnetic properties of materials. In this thesis, LaNiO_3 (LNO) ultrathin films and LaNiO_3/LaMnO_3 (LNO/LMO) superlattices have been prepared, and their electrical and magnetic properties have been studied by means of strain and size effects. The transport characteristics and magnetic properties of the buffer layer are regulated by the insertion of the buffer layer and the design of the superlattice structure. The main works are as follows: (1) A series of LNO ultrathin films with different thickness have been epitaxially grown on (001) direction SrTiO_3 (STO) and LaAlO_3 (LAO) single crystal substrates by pulsed laser deposition (PLD) and reflection high energy electron diffractometer (RHEED). The LNO film on STO substrate is subjected to tensile stress. Atomic force microscopy (AFM) (AFM) characterization shows that the ultrathin film has a flat surface with atomic level. The transport characteristic test shows that the film resistance increases with the decrease of film thickness. When the thickness is less than a certain critical value, LNO changes from metal state to insulating state. The critical thickness on STO and LAO substrates is 5 and 4 (u. C.), respectively. The fitting results of the surface resistance-temperature curve indicate that the reason of the transition is the localization effect of carriers in the LNO film. (2) at 5u. C. The thick LNO film is intercalated with the STO substrate by 2u. C. The transport characteristics of thick STO films as buffer layer have changed obviously. When the temperature is above 100K, the (XPS) analysis of LNO changes from insulating state to metal state. (XPS) analysis shows that the oxygen vacancy in STO films grown under low oxygen pressure (10-3mbar) can be attributed to the oxygen vacancies in STO films. Oxygen vacancies provide a large number of electrons, which transfer from the STO layer to the LNO layer, which inhibits the localization of carriers in the LNO layer. The oxygen vacancies in STO thin films were greatly reduced by annealing and increasing oxygen pressure. (3) [(LNO) m / (LMO) n] x superlattice films were grown on (111) direction STO single crystal substrates by PLD. The magnetic measurement results show that the exchange bias exists in the system containing paramagnetic interface at low temperature, which may be due to the ferromagnetic interaction caused by charge transfer at the interface. After changing the number of layers of x and LNO components, the exchange bias field HE and coercive field HC of superlattice change, which is shown as follows: with the decrease of the number of layers of x and LNO component m, the exchange bias field of superlattice changes. The exchange bias field HE and coercive field HC both become smaller.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.2
，
本文编号：2146441
[Abstract]:In recent years, perovskite-related oxide materials, represented by nickel, have been a hot topic in condensed matter physics and material science. In perovskite nickel heterostructure, the strong interaction between lattice, charge, spin and orbital degree of freedom makes the material have complex physical properties. These degrees of freedom can be regulated by means of strain, size and superlattice structure design, which can control the electrical and magnetic properties of materials. In this thesis, LaNiO_3 (LNO) ultrathin films and LaNiO_3/LaMnO_3 (LNO/LMO) superlattices have been prepared, and their electrical and magnetic properties have been studied by means of strain and size effects. The transport characteristics and magnetic properties of the buffer layer are regulated by the insertion of the buffer layer and the design of the superlattice structure. The main works are as follows: (1) A series of LNO ultrathin films with different thickness have been epitaxially grown on (001) direction SrTiO_3 (STO) and LaAlO_3 (LAO) single crystal substrates by pulsed laser deposition (PLD) and reflection high energy electron diffractometer (RHEED). The LNO film on STO substrate is subjected to tensile stress. Atomic force microscopy (AFM) (AFM) characterization shows that the ultrathin film has a flat surface with atomic level. The transport characteristic test shows that the film resistance increases with the decrease of film thickness. When the thickness is less than a certain critical value, LNO changes from metal state to insulating state. The critical thickness on STO and LAO substrates is 5 and 4 (u. C.), respectively. The fitting results of the surface resistance-temperature curve indicate that the reason of the transition is the localization effect of carriers in the LNO film. (2) at 5u. C. The thick LNO film is intercalated with the STO substrate by 2u. C. The transport characteristics of thick STO films as buffer layer have changed obviously. When the temperature is above 100K, the (XPS) analysis of LNO changes from insulating state to metal state. (XPS) analysis shows that the oxygen vacancy in STO films grown under low oxygen pressure (10-3mbar) can be attributed to the oxygen vacancies in STO films. Oxygen vacancies provide a large number of electrons, which transfer from the STO layer to the LNO layer, which inhibits the localization of carriers in the LNO layer. The oxygen vacancies in STO thin films were greatly reduced by annealing and increasing oxygen pressure. (3) [(LNO) m / (LMO) n] x superlattice films were grown on (111) direction STO single crystal substrates by PLD. The magnetic measurement results show that the exchange bias exists in the system containing paramagnetic interface at low temperature, which may be due to the ferromagnetic interaction caused by charge transfer at the interface. After changing the number of layers of x and LNO components, the exchange bias field HE and coercive field HC of superlattice change, which is shown as follows: with the decrease of the number of layers of x and LNO component m, the exchange bias field of superlattice changes. The exchange bias field HE and coercive field HC both become smaller.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.2
，
本文编号：2146441
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