尖晶石结构Cr基氧化物局域晶格畸变的电子顺磁共振研究

The frustration and the competition and collaboration among the charge, orbital, spin and lattice degree of freedom may lead to the appearance of lots of interesting physical phenomena in spinel chromium oxides. Now there are some basic physical issues are not clear in these materials, for example, the mechanism of the multiferroics and magnetoelectric effect in spinel chromium oxides and the relationship between the local lattice distortion and macroscopic quantum order. The electron paramagnetic resonance (EPR) is a useful tool to probe the local lattice distortion in condensed mater materials. The magnetic resonance equipment in the high magnetic field lab, Chinese Academy of Science provides a good platform and opportunity for the applicants to carry out the related work. The project aiming at the cultivation projecting-steady state high magnetic-field magnetic resonance technology, intends to study the EPR of CoCr2O4 single crystal and MnCr2O4 one. The local lattice distortion can be introduced by treating the single crystal in different atmosphere and the chemical substitution of Co and Cr sites of CoCr2O4 single crystal. Comparing EPR line width parameters of the pure and the different doping ions in CoCr2O4 single crystal and isostructural MnCr2O4 one, the applicants will study the relationship between the local lattice distortion and quantum order in spinel chromium oxides. The proposal is expected to lay the foundation for the deeper understanding and study of the mechanism of multiferroics and magnetoelectric effect and the spin dynamics in the low temperature in spinel chromium oxides.

尖晶石结构Cr基氧化物存在阻挫以及电荷、自旋、轨道和晶格多种自由度竞争与合作，表现出丰富的物理现象。目前该体系中许多基本的物理问题如多铁性和磁电耦合效应的起因、局域晶格畸变与宏观量子有序态之间存在怎样的密切的关系等还不完全清楚。电子顺磁共振(EPR)技术是探测晶格畸变的有力手段。依托合肥物质科学研究院而建立的稳态强磁场磁共振技术为申请者开展相关工作提供了很好的平台和契机。本申请项目依托稳态强磁场EPR，拟选取尖晶石结构CoCr2O4和MnCr2O4单晶样品为研究对象，通过对CoCr2O4单晶样品的不同后处理、Co位和Cr位进行不同元素替代，引入局域晶格畸变，研究其EPR线宽参数的变化规律。同时对比研究同结构MnCr2O4单晶的谱线，建立局域晶格畸变与宏观量子有序态的关系。本项目的研究将为深入理解该体系中多铁性、磁电耦合效应的起源和低温自旋动力学行为奠定一定基础。

尖晶石结构Cr 基氧化物中由于电荷、自旋、轨道和晶格等多种自由度间的竞争与合作，使得体系表现出及其丰富的物理性质，比如阻挫、多铁性及多种复杂磁有序等。本项目系统研究了尖晶石结构Cr基氧化物的晶体结构、磁、电输运等基本物性，利用电子顺磁共振的方法探测体系中局域晶格畸变和其宏观物性的关系。在MnCr2O4中，通过电子自旋共振的方法揭示了该体系中强自旋晶格耦合作用是体系在低温下出现螺旋亚铁磁结构的主要原因。通过Zn离子替代Mn离子，我们系统研究了Mn1-xZnxCr2O4体系的磁性质演变过程。通过调整生长工艺，我们生长了缺陷少和氧含量接近名义组分的高质量MnCr2O4，并在低温下观察到新的结构相变并伴随有多铁性的出现。利用太赫兹技术，研究了CoCr2O4单晶中不同亚晶格随温度的演变过程，并观察到了法拉第效应。本项目取得的研究结果对尖晶石结构Cr基氧化物体系研究具有重要的推动作用，为今后对该领域的深入研究提供重要信息，对该体系中多铁性的起源提供了重要的参考依据。