兰州大学机构库 >物理科学与技术学院
铁基高温超导的穆斯堡尔谱研究
Alternative TitleMossbauer study of Iron-Based High-Tc superconductors
柳祥
Thesis Advisor庞华
2015-05-25
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword穆斯堡尔谱 铁基超导体 磁相变 SDW 坍塌相变 磁涨落 铁基超导 共掺杂 结构相变 超导相变 超精细相互作用 磁性
Abstract在铁基超导体中,磁性、超导电性、晶格不稳定性通常密切相关,通过研究三者之间的关系,对研究高温超导机制以及发现新型超导材料有着重要意义。本文中,我们用FeAs助溶剂法制备了高质量的Ca1-xNdxFe2As2(x=0.05,0.15)、Ca1-xPrxFe2As2(x=0.075,0.13)和Ca1-xCexFe2As2(x=0.09,0.2)单晶,并用穆斯堡尔谱仪对其进行了系统的测试与分析。Ca1-xNdxFe2As2(x=0.05,0.15)单晶两个样品在低温下都有顺磁相和SDW两个相。Ca0.85Nd0.15Fe2As2发生了超导相变,相变温度为38K,在超导温度之下,磁性相与超导相共存,谐波振幅h3为负值,SDW形状为准三角形。通过临界指数模型拟合发现随着Nd掺杂量的增加,指数β由0.07增大到0.16,加强了Fe原子磁相互作用的2D特征,抑制了层间磁交换。另外,超导体Ca0.85Nd0.15Fe2As2中的顺磁相随着温度降低发生坍塌相变。通过第一性原理的方法计算了Ca1-xRexFe2As2体系中Fe的电子结构和电场梯度EFG,研究证实了Ca0.87Pr0.13Fe2As2样品在低温下有高自旋Fe原子环境和非磁性相两个环境,两种Fe原子环境以约3:7的比例共存。其中低自旋Fe原子体系在77K到60K之间的某一温度处发生坍塌相变。而高自旋Fe原子磁矩随温度降低出现磁涨落,并且超导相与磁涨落共存。Ca0.8Ce0.2Fe2As2单晶在低温下也有两种Fe环境:非磁性相和高自旋Fe原子环境。其中高自旋Fe原子磁矩出现磁涨落,随温度降低磁涨落增强,在超导转变温度之下,超导相与磁涨落共存。
Other AbstractThe magnetism, superconductivity, lattice instability usually closely related to each other in the iron-based superconductors. It's of fundamental importance to clarify the relationship mong them in exploreing the high-temperature superconductivity mechanism.In this thesis, we prepared single crystals of Ca1-xNdxFe2As2(x=0.05,0.15), Ca1-xPrxFe2As2(x=0.075,0.13) and Ca1-xCexFe2As2(x=0.09,0.2) with high quality by FeAs self-solvent method, and investigated the hyperfine interactions of these compounds systematically by Mössbauer spectrometer.It is found that the single crystals of Ca1-xNdxFe2As2 (x = 0.05, 0.15) have two phases at low temperatures, paramagnetic phase and antiferrmatic spin density wave phase (SDW). Superconducting phase transition occurs at Tc = 38K for Ca0.85Nd0.15Fe2As2 single crystal. The magnetic phase and superconducting phase coexistence at the temperatures below Tc. The harmonic amplitude h3 behaves negative and the shape of the SDW becomes quasi-triangle then. We found the index β increased to 0.16 from the 0.07 with with increasing Nd doping by Ising model, indicating the strengthening of the 2D features of the magnetic interaction between Fe moments and the suppressing of interlayer magnetic exchange by Nd doping. In addition, with decreasing temperature, the paramagnetic phase experiences collapsed phase transition in Ca0.85Nd0.15Fe2As2 single crystal.According to the theoretical calculations of the electronic structures and the electric field gradient (EFG) of Ca1-xRexFe2As2, it is confirmed that there exist two local environments of Fe ions in Ca0.85Nd0.15Fe2As2 single crystal at low temperature, one is composed of high spin Fe atoms, the other is non-magnetic. And the two kinds of Fe ions coexist with each other with the ratio of 3 : 7. Collapsed phase transition occurres at some temperature between 60K and 77K in non-magnetic phase. While it appeared the magnetic fluctuations emerges with the decreasing temperature in the Fe ions with high spin. And superconducting phase coexist with magnetic fluctuations below Tc.Finally, there are two Fe environments in Ca0.8Ce0.2Fe2As2 single crystals at low temperatures, non-magnetic phase and the phase with Fe ions at high spin state. Magnetic fluctuations happens in the high spin Fe atoms, and is enhanced with decreasing temperature. And superconductivity coexists with magnetic fluctuations under the superconducting transition temperature in this comound.
URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/229266
Collection物理科学与技术学院
Recommended Citation
GB/T 7714
柳祥. 铁基高温超导的穆斯堡尔谱研究[D]. 兰州. 兰州大学,2015.
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