掺杂锰氧化物薄膜的溶胶-凝胶法制备及其物理特性

发布时间：2019-04-17 12:45

【摘要】：钙钛矿结构锰氧化物(La1-xAxMnO3, A=Sr, Ca, Ba等),由于具有庞磁阻效应、磁致伸缩效应等丰富的物理特性,在磁存储器件、磁传感器件、自旋阀等方面具有重大的潜在应用价值,同时该体系又是电荷、自旋、晶格、轨道自由度高度关联的强关联体系,蕴藏着十分丰富的物理内容,是凝聚态物理的理论研究及器件应用方面的研究热点。本论文采用溶胶-凝胶法制备La1-xAxMnO3薄膜,通过研究该材料制备工艺与显微结构的依赖关系及影响规律,系统研究化学组分、界面应力、退火氛围等对薄膜物理特性影响机制,探讨磁性能与电输运特性的物理关联机制。本论文所获得的一些结果如下：1、Sr掺杂La0.7Ca0.3-xSrxMnO3薄膜的磁电阻调控特性和机制多晶LCSMO薄膜的Tc和TMI均表现出随Sr掺杂浓度增加而单调增加的特性,而其电阻率则随Sr掺杂浓度增加而降低。按照磁电阻特性随温度的变化规律,LCSMO薄膜以Sr掺杂浓度分为两类：掺杂浓度较低(x≤0.05)时,薄膜磁电阻随温度呈现先缓慢减小然后增加的趋势,并在TMI附近到最大值,表明在TMI附近的金属-绝缘体相变过程中的相分离过程的无序效应对磁电阻贡献较大；当掺杂浓度较高(x≥0.1)时,薄膜磁电阻随温度升高单调减小,表明低温下的晶界隧穿对磁电阻贡献较大。按照磁电阻特性随磁场的变化规律,LCSMO薄膜以TMI温度为界表现不同：当温度低于TMI时,磁电阻随磁场变化呈双梯度线性关系,低磁场时晶界隧穿效应起主导,该部分效应对磁场特别敏感,高磁场时磁电阻主要来源于磁场对自旋波动的压制；当温度高于TMI时,LCSMO薄膜的磁电阻均随着磁场近乎线性变化,磁电阻主要来源于磁场对自旋波动的压制。2、具有高度择优取向的La0.7Ca0.25Sr0.05MnO3薄膜的溶胶-凝胶法制备采用溶胶-凝胶法在不同衬底(SrTiO3和LaAlO3)上成功制备了具有高度择优取向的La0.7Ca0.25Sr0.05MnO3 (LCSMO)薄膜,在不同衬底上制备的LCSMO薄膜的居里温度、磁性和磁电阻特性相似,在室温附近都表现出较大磁电阻(285K,3T, MR=50%)。与多晶样品相比,具有高度择优取向的LCSMO薄膜的金属-绝缘转变温度(TMI)与其居里温度(Tc)很接近。单晶LCSMO的磁电阻主要源于居里温度附近磁场导致的从金属电子电导到小极化子跳跃电导的转换,而多晶样品的磁阻主要来源于载流子的晶界隧穿。3 La0.7Sr0.3MnO3薄膜的磁学特性和机制探讨通过不同氛围(空气、氧气、氮气)中的退火,对所制备La1-xSRxMnO3+8薄膜的Mn4+/Mn3+比率进行了调控。退火氛围对薄膜的晶体结构没有产生明显影响。当δ＝0时,Mn4+/Mn3+=1:2氧气氛中退火,高的氧含量增加了Mn4+/Mn3+的比率,使得有更多的Mn4+参与到Mn4+与Mn3+之间双交换作用,使得磁有序度增加,居里温度随着LSMO薄膜的铁磁有序度的增加而有所增加(Tc-空气=339K,Tc-氧气=354K)。氮气氛围退火下的La0.7Sr0.3MnO3薄膜的降低了Mn4+/Mn3+的比率,使得有更多的Mn4+参与到Mn4+与Mn4+之间的超交换作用使得反铁磁相居于主导地位,进而由于反铁磁绝缘相的存在使得样品近乎绝缘。空气和氧气退火氛围下,LSMO的电阻率变化曲线相似,而且金属-绝缘转变温度TMI几乎相同。
[Abstract]:The perovskite structure manganese oxide (La1-xAxMnO3, A = Sr, Ca, Ba, etc.) has a great potential application value in the aspects of magnetic memory device, magnetic sensor device, spin valve and the like due to the rich physical characteristics of the surface magneto-resistance effect and the magnetostriction effect, The strong association system, which is highly correlated with the lattice and the degree of freedom of the orbit, contains abundant physical contents, and is a hot topic in the theoretical research of condensed matter physics and the application of the device. In this paper, La1-xAxMnO3 thin films were prepared by sol-gel method, and the influence mechanism of chemical composition, interface stress and annealing atmosphere on the physical properties of the film was studied by studying the dependence of the material preparation technology and the microstructure. The physical association mechanism of the properties of the magnetic energy and the electric transport is discussed. The results of this paper are as follows:1, Sr-doped La0.7Ca0.3-xSrxMnO3 thin film's magnetic resistance control characteristic and mechanism polycrystalline LCSMO thin film's Tc and TMI show the characteristics of increasing monotonously with the increase of Sr doping concentration, while the resistivity decreases with the increase of Sr doping concentration. according to the change law of the magnetic resistance characteristic with the temperature, the LCSMO thin film is divided into two types by the Sr doping concentration: when the doping concentration is lower (x-0.05), the magnetic resistance of the thin film first slowly decreases and then increases with the temperature, and reaches the maximum value in the vicinity of the TMI, It is shown that the disorder effect of the phase separation process in the phase transition process of the metal-insulator near the TMI has a great contribution to the magnetic resistance; when the doping concentration is higher (x = 0.1), the magnetic resistance of the thin film decreases monotonically with the temperature, indicating that the grain boundary tunneling at low temperature contributes greatly to the magnetic resistance. according to the change law of the magnetic resistance characteristic along with the magnetic field, the LCSMO film is distinguished by the TMI temperature: when the temperature is lower than the TMI, the magnetic resistance is in a double-gradient linear relationship with the change of the magnetic field, the grain boundary tunneling effect is dominant when the low magnetic field is low, the partial effect is particularly sensitive to the magnetic field, When the temperature is higher than TMI, the magnetic resistance of the LCSMO film changes linearly with the magnetic field, and the magnetic resistance mainly comes from the suppression of the spin fluctuation of the magnetic field. La0. 7Ca0. 25Sr0. 05MnO3 (LCSMO) films with highly preferred orientation were prepared on different substrates (SrTiO3 and LaAlO3) by sol-gel method with highly preferred La0.7Ca0. 25Sr0. 05MnO3 thin films. The Curie temperature, magnetic and magnetic resistance characteristics of LCSMO films prepared on different substrates were similar. A large magnetic resistance (285K, 3T, MR = 50%) was exhibited near room temperature. The metal-insulated transition temperature (tmi) of the LCSMO thin film having a highly preferred orientation is very close to its Curie temperature (Tc) as compared to a polycrystalline sample. The magnetic resistance of the single crystal LCSMO is mainly due to the transition from the electronic conductivity of the metal to the small-polarization sub-jump conductance due to the magnetic field near the Curie temperature, and the magnetic resistance of the polycrystalline sample mainly comes from the grain boundary tunneling of the carriers. The magnetic properties and the mechanism of the 3La0.7Sr0. 3MnO3 thin film are discussed through different atmospheres (air, oxygen, The Mn4 +/ Mn3 + ratio of the prepared La1-xSRxMnO3 + 8 film was controlled by annealing in nitrogen. The annealing atmosphere does not have a significant effect on the crystal structure of the film. when n = 0, the Mn4 +/ Mn3 + = 1:2 oxygen atmosphere is annealed, the high oxygen content increases the ratio of Mn4 +/ Mn3 +, so that more Mn4 + is involved in the double-exchange action between the Mn4 + and the Mn3 +, so that the magnetic order degree is increased, The Curie temperature increased with the increase of the ferromagnetic order of the LSMO film (Tc-air = 339 K, Tc-oxygen = 354 K). The ratio of Mn4 +/ Mn3 + is reduced by the La0.7Sr0. 3MnO3 thin film under the nitrogen atmosphere, so that more Mn4 + is involved in the super-exchange between the Mn4 + and the Mn4 +, so that the anti-ferromagnetic phase is dominant, and the sample is almost insulated due to the existence of the anti-ferromagnetic insulating phase. The resistivity change curves of the LSMO are similar in the air and oxygen annealing atmosphere, and the metal-insulated transition temperature TMI is almost the same.
【学位授予单位】：华东师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.2

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