【作者】 张仕乐；

【导师】 张裕恒；

【作者基本信息】 中国科学技术大学 ， 凝聚态物理， 2011， 博士

【摘要】 钙钛矿型过渡族金属氧化物是一种典型强关联体系材料,由于具有超导电性、庞磁电阻、反常霍尔效应、大的热电效应、多铁等奇异物理性质,因而被人们广泛的研究。钙钛矿型过渡族金属氧化物中电荷、轨道、自旋以及声子之间的相互作用使得体系呈现出许多有趣的物理现象,例如电荷有序、轨道序、自旋序、玻璃态、相分离、金属绝缘体转变、自旋态转变等。这些有趣物理现象同凝聚态物理的许多基本问题紧密相关,例如杂化理论,理解这些问题的微观机理的会对凝聚态物理的发展起到巨大的推动作用。本文中我们选取了不同dp杂化程度的钙钛矿型过渡金属氧化物材料为研究对象,用高压和掺杂手段调制杂化,进而研究材料的物理性质。首先我们简要的回顾了强关联电子体系以及各种电子间相互作用的理论和使用范围。综述了钙钛矿过渡金属氧化物材料的历史与发展;介绍了钙钛矿过渡金属氧化物材料的晶体结构,电子结构,氧位移偏移,输运性质,有序相和相分离等,并对这些结构和性质作了初步的理论解释。然后重点对钙钛矿过渡族金属Fe氧化物钻,Ru氧化物和Co氧化物物理性质作了详细的介绍。我们系统的研究了dp杂化程度较低的La_0.5Ba_0.5FeO₃体系的电荷、自旋和晶格之间相互作用。发现体系的电磁性质与电荷歧化效应强烈关联,高压下体系的磁性结果表明低温下Fe3+发生了自旋态转变。这是由于压力使得晶场能提高,杂化变强造成的。我们设计和对比研究Sr_1-xCa_xRu_1-xCr_xO₃和Sr_1-xLa_xRu_1-xCr_xO₃两组体系的磁性和输运性质。我们找到了杂化强的SrRuO₃（4d电子中唯一具有长程磁有序材料）体系中唯一的离子掺杂（Cr）使其磁有序升高的原因:体系中的Ru⁺⁵-O-Cr⁺³超交换铁磁相互作用。我们系统的研究了Ti掺杂La_0.5Ba_0.5Co_1-xTi_xO₃体系的磁效应。结果表明体系中两种Co离子自旋态没有发生变化,一直处于中自旋态。B位引入Ti离子,撑大了晶格,增加了Co-O键键长,削弱了双交换相互作用,降低铁磁温度。当铁磁相互作用降到某一阈值,体系中出现了反铁磁相互作用。低温下铁磁相互作用和反铁磁相互作用的竞争引入了再入自旋玻璃态。由此,我们建立了一个磁相图。我们系统的研究了多种离子掺杂钴氧化物La_0.5Ba_0.5Co_0.9R_0.1O₃ （R= Zn, Cu,Ni, Ru, Ti, and Cr）的磁性。研究表明所有掺杂样品中两种Co离子都处于中自旋态。对于,Cu,Zn,Ni,Ti和Ru离子掺杂,体系的铁磁温度都降低了且呈现出复杂的磁性。不同掺杂带来不同的结果这与Co³⁺/Co⁴⁺,＜TB＞, f和掺杂离子的巡游性有关。值得注意的是B位掺杂唯有Cr离子使得TC上升。这是由于体系中存在Co-O-Cr相互作用,从而提高了磁有序温度。ESR实验证实了这一结论。可以推出铁磁交换相互作用来自Cr³⁺(t_2g³e_g⁰)-O-Co³⁺(t_2g⁵e¹_g) andCr³⁺(t³_2ge_g⁰)-O-Co⁴⁺(t⁴_2ge_g¹)。更多还原

【Abstract】 The transition metal oxides have been widely studied due to their novel properties,such as superconductivity, colossal magnetoresistance, abnormal Hall effect, huge thermoelectricaleffect and multiferronics. In these system charge, orbital，spin and latticeare coupled to each other,and complicated phase diagrams are introduced the competitionamong these interactions, giving rise to some interesting phenomena such as chargeordering, magnetic ordering, glassy behavior, phase separation, metal-insulator transitionand spin-state transition. Therefore，further understanding of their underlyingPhysical mechanism, such as hybirdizition, wil1 greatly boarden our knowledge on thecondensed mater Physics.In this dissertation, three materials of different p-d hybirdizition are as research objects.We regulate the hybirdizition with high pressure and doping methods, then studythe physical properties of the material. We briefly review the strong correlation systemand the various interactions between electronics. We present a review of the historyand progress of the Perovskite Transition Metal Oxides. Then, we introduce the physicalproperties of Perovskite Transition Metal Oxides，which includes the structuralconsiderations，electronic considerations, electronic considerations, oxygen displacements,transport properties，ordered phase and phase separation. Last, we focus on thephysical properties of iron-based , ruthenium-based and cobalt-based perovskites.We systematically researched charge, spin and lattice interactions in La_0.5Ba_0.5FeO₃of the low levels p-d hybirdizition system. The resistivity and magnetism were strongcorrelation with charge disproportion. The spin state transition of Fe³⁺ at under highpressure-low temperature is found in the magnetization measurement , which is due tothe pressure enlarged the crystal field energy and strengthen the hybirdizition.The electromagnetic property of two series of samples Sr_1-xLa_xRu_1-xCr_xO₃（SCRC）和Sr_1-xCa_xRu_1-xCr_xO₃ （x= 0.04, 0.08 and 0.12） have been designed and investigated.We found the reason of enhancing the ferromagnetism in the SrRu_1-xCr_xO₃system, that is Ru⁵⁺-O^2-Cr³⁺ superexchange interaction.A detailed magnetic study has been carried out for the Ti-doped La_0.5Ba_0.5Co_1-xTi_xO₃（x=0, 0.05, 0.075, 0.10, 0.125 and 0.15） cobaltites. The spin states of Co ions does notchange and stabilize in the intermediate spin state. With introducing Ti ions at B site,it enlarged the crystal constant and Co-O bond length. Then it weakened the doubleexchange interaction and the ferromagnetic Curie temperature. When ferromagnetic interaction weakened to a threshold, antiferromagnetic exist in the system. At low temperature,the system is in a reentrant spin glass state due to the competition between theferromagnetic interaction and the antiferromagnetic interaction. Thus, we established amagnetic phase diagram.A magnetic study has been carried out for the R-doped La_0.5Ba_0.5Co_0.9R_0.1O₃（R=Cu, Zn, Cr, Ni, Ti and Ru） cobaltites. All ions doping stabilized the intermediatespin state of both kinds of Co ions. For R = Zn²⁺, Cu²⁺, Ni³⁺, Ti⁴⁺ and Ru⁴⁺, it decreasesTC and presents a complex magnetism which are closely related to Co3+/Co4+,the B site average cationic radius（.rB.）, the tolerance factor（f） and ions itinerant character.Whereas in contrast, doping with Cr³⁺ increases TC. We presume that the Co-OCrexchange interaction exists in system and enhances the ordering temperature. Thisinteraction is confirmed experimentally by ESR spectra. It can deduce that the ferromagneticexchange interaction comes from Cr³⁺(t_2g³e_g⁰)-O-Co³⁺(t_2g⁵e¹_g) andCr³⁺(t³_2ge_g⁰)-O-Co⁴⁺(t⁴_2ge_g¹)。更多还原