Spin-Charge-Lattice Couplings in the Mn Oxide Systems

取代的镧锰酸盐（准立方和层状化合物）提供了一个不寻常的机会，可以在局部结构水平上研究自旋-电荷-晶格相关性，并将其与巨磁电阻（CMR）和电荷有序（CO）等宏观现象联系起来。局部探针研究（扩展x射线吸收精细结构（EXAFS）和中子对分布函数（PDF）分析）表明，随着温度的升高，通过零场的铁磁转变温度Tc，存在显著的极化子诱导的结构变化。此外，还有一个大而反常的磁致伸缩与CMR行为有关。该个人研究者奖支持了一个项目，该项目首次确定了磁场引起的局部结构变化，并将EXAFS测量扩展到几个层状化合物。高场测量将探测在Tc以下初始磁化是如何发展的。对层状材料的测量将确定局部畸变的各向异性。这些结果对于在这些系统中建立更好的铁磁性和电输运模型具有重要意义。建议的项目将提供一个研究生的论文题目，以及几个本科生的高级论文题目。学生们将在PI的领导下以团队的形式工作。他们将获得在国家机构进行研究的经验。当样品在低温下磁化时，一些被取代的镧锰（部分La被Ca或Sr取代）显示出Mn-O键局部原子畸变的不寻常的减少。对于接近磁转变温度的温度，样品的电阻率也有很大的变化，并且有很大的异常磁致伸缩（施加磁场时样品尺寸的变化）。该个人研究者奖支持一个项目，研究在大的外加磁场中局部畸变如何变化，并将这些结果与样品磁化、磁致伸缩和电阻率联系起来。这些结果还应该确定磁化过程的初始阶段如何在这些材料中发生。类似的测量也将在层状锰矿化合物上进行，但这里需要分别确定层内和垂直于层的扭曲程度。建议的项目将提供一个研究生的论文题目，以及几个本科生的高级论文题目。学生们将在PI的领导下以团队的形式工作。他们将获得在国家机构进行研究的经验。

The substituted Lanthanum manganites (quasicubic and layered compounds) provide an unusual opportunity to investigate spin-charge-lattice correlations at the local structure level and connect the correlations with macroscopic phenomena such as Colossal Magnetoresistance (CMR) and charge ordering (CO). Local probe studies (Extended X-ray Absorption Fine Structure (EXAFS) and neutron Pair Distribution Function (PDF) analysis) show that there is a significant, polaron-induced, structural change as the temperature is increased through the ferromagnetic transition temperature, Tc, in zero field. In addition, there is a large and anomalous magnetostriction that is connected with the CMR behavior. This individual investigator award supports a project to determine for the first time the field-induced changes in the local structure as a function of magnetic field and extend the EXAFS measurements to several of the layered compounds. The high field measurements will probe how the magnetization initially develops just below Tc. The measurements on the layered materials will determine the anisotropy of the local distortions. These are important results for developing better models of ferromagnetism and electrical transport in these systems. The proposed project will provide the thesis topic for a graduate student as well as several senior thesis topics for undergraduates. The students will work as a team under the PI. They will gain the experience of performing research at a national facility.Some of the substituted the Lanthanum manganites (with part of the La replaced with Ca or Sr) show an unusual decrease in the local atomic distortions of the Mn-O bond as the sample becomes magnetized at low temperatures. For temperatures near the magnetic transition temperature there is also a large change in the resistivity of the sample and a large anomalous magnetostriction (a change in sample size when a magnetic field is applied). This individual investigator award supports a project to investigate how the local distortion changes in a large applied magnetic field and to correlate these results with the sample magnetization, magnetostriction and electrical resistivity. These results should also determine how the initial stages of the magnetization process take place in these materials. Similar measurements will be carried out on a layered manganite compound - but here the distortions in the layers and perpendicular to the layers need to be determined separately. The proposed project will provide the thesis topic for a graduate student as well as several senior thesis topics for undergraduates. The students will work as a team under the PI. They will gain the experience of performing research at a national facility.