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首页> 外文学位 >Temperature-dependent local atomic structure in the colossal magnetoresistive manganese oxide lanthanum strontium manganese oxide.
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Temperature-dependent local atomic structure in the colossal magnetoresistive manganese oxide lanthanum strontium manganese oxide.

机译：巨大的磁阻氧化锰镧锶锰氧化物中随温度变化的局部原子结构。

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摘要

Extended X-ray Absorption Fine Structure (XAFS) measurements at the Mn, Sr, and La K-edges of the colossal magnetoresistive (CMR) manganese oxide La1.2Sr1.8 Mn2O7 show that the local atomic structure is coupled to the metal-insulator and paramagnetic-ferromagnetic transitions. These polarized and temperature dependent XAFS measurements are the first performed on a layered CMR manganite in an effort to further elucidate the strong interplay between charge, spin, and lattice degrees of freedom in these hole doped oxides. The polarization dependence of the XAFS indicates that the local distortions accompanying this electronic and magnetic phase transition are associated with Jahn-Teller type distortions to the apical (lying perpendicular to the perovskite MnO planes) oxygen distribution around the MN cations. The metal-insulator transition is accompanied by a sudden increase in the number of Jahn-Teller distorted Mn sites as well as anomalous increases in the thermal Debye-Waller factor indicating increased fluctuations of the local atomic arrangements. A possibility for the La and Sr cations to influence the electronic and magnetic transitions is suggested by their tendency to stabilize differing local arrangements of the nearest neighbor oxygen atoms. The contrasting temperature dependence of the La-oxygen and Sr-oxygen distributions shows that the temperature dependent local atomic distortions observed in the apical oxygen distribution around the Mn ions are primarily associated with Sr atoms. The observed differences in the local atomic structures surrounding Sr and La are supported by similar results in the non-CMR oxide LaSrMnO4. This element specific interaction suggests the possibility that the local dopant concentration could enhance or induce electronic, magnetic, and structural phase separation. Thus, the XAFS experiments documented here have supported the general view that local lattice distortions can play a role in the MI transition and the CMR effect in the bilayer manganite La1.2 Sr1.8Mn2O 7 while also indicating that the effects of the local chemical environment of the Mn ions may play a role in determining the nature of the phase transitions.
机译：巨大的磁阻（CMR）氧化锰 La 1.2 的Mn，Sr和La K边缘的扩展X射线吸收精细结构（XAFS）测量Sr 1.8 Mn 2 O 7 显示局部原子结构耦合到金属绝缘体和顺磁-铁磁跃迁。这些极化和温度相关的XAFS测量是首先在层状CMR锰矿上进行的，目的是进一步阐明这些空穴掺杂氧化物中电荷，自旋和晶格自由度之间的强相互作用。 XAFS的极化相关性表明，伴随着这种电子和磁性相变的局部畸变与MN阳离子周围的顶端（垂直于钙钛矿MnO平面分布）氧分布的Jahn-Teller型畸变相关。金属-绝缘体的转变伴随着Jahn-Teller扭曲的Mn位点数量的突然增加，以及热Debye-Waller系数的异常增加，表明局部原子排列的波动增加。 La和Sr阳离子可能会稳定最近邻氧原子的不同局部排列，因此有可能影响其电子和磁性跃迁。 La氧和Sr氧分布的对比温度依赖性表明，在Mn离子周围的顶部氧分布中观察到的与温度有关的局部原子畸变主要与Sr原子有关。在非CMR氧化物 LaSrMnO 4 中相似的结果支持了Sr和La周围的局部原子结构的观察到的差异。这种元素特异性的相互作用暗示了局部掺杂剂浓度可以增强或诱导电子，磁性和结构相分离的可能性。因此，这里记录的XAFS实验支持了以下普遍观点：局部晶格畸变可以在双层锰的 La 1.2 Sr 1.8 Mn 2 O 7 ，同时还指出Mn离子的局部化学环境的影响可能在确定相变的性质中起作用。

著录项

  • 作者

    Villella, Phillip Michael.;

  • 作者单位

    University of Colorado at Boulder.;

  • 授予单位 University of Colorado at Boulder.;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2002
  • 页码 189 p.
  • 总页数 189
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 O49;
  • 关键词

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