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Correlation between electrical and magnetic properties in alkali and alkaline earth metal doped lanthanum manganites.

机译：碱金属和碱土金属掺杂镧锰矿中电和磁性能之间的相关性。

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摘要

The recent colossal magnetoresistance (CMR) found in cation doped lanthanum manganites (La,A)MnO3, where A is the cation, has evoked great interest either in possible applications or fundamental studies. The CMR manganite undergoes a paramagnetic-ferromagnetic (PM-FM) transition along with an insulator-metal (I-M) transition when it is cooled below its Curie temperature. Such a concurrence of PM-FM and I-M transitions in the CMR manganites was first qualitatively explained in the “double exchange” (DE) theory, proposed by Zener in 1951.; In the search of the correlation between electrical and magnetic transport properties in the CMR manganites, a molecular field approximation was then used by Searle and Wang to calculate the magnetization and resistivity and compared to the experimental data obtained from La1-xPbxMnO 3 single crystals. Although the data fit the molecular field calculation well, it remains an open question whether such a molecular field approximation can be applied to other CMR lanthanum manganites. It is our intention to do a thorough and systematic study of the cation doped lanthanum manganites and to compare the resistivity and magnetization obtained from these materials to the molecular field calculation. The materials we choose are the alkali and alkaline earth metal doped lanthanum manganites, La 1-xAxMnO3, where x = 1/3 for A = Ca, Sr, and Ba; x = 1/6 for A = Na, K, Rb, and Cs. The hole doping level is the same for all the materials we study in this way. It also avoids any complexity which arises from multi-cation doping such as La1-x-yYyCaxMnO 3. Due to the difficulty of growing alkali metal doped lanthanum manganites, we chose to fabricate thin films instead. The thin films are fabricated by the e-beam/thermal co-evaporation method that has been proved to be suitable in these materials.; The magnetization as a function of temperature M(T) in all the CMR manganite thin films matches well the molecular field calculation, but the resistivity versus temperature ρ(T) cannot be explained by the theory. A simple explanation is given in chapter 5.
机译：最近在阳离子掺杂的镧系锰（La，A）MnO 3 （其中A为阳离子）中发现的巨大磁阻（CMR）在可能的应用或基础研究中引起了极大的兴趣。当CMR锰矿冷却至居里温度以下时，它会经历顺磁-铁磁（PM-FM）转变以及绝缘体-金属（I-M）转变。最早在1951年齐纳（Zener）提出的“双交换”（DE）理论中，定性地解释了CMR锰矿中PM-FM和I-M过渡的同时存在。在寻找CMR锰矿中电和磁传输特性之间的相关性时，Searle和Wang使用分子场近似来计算磁化强度和电阻率，并与从La <1-x < / sub> Pb x MnO 3 单晶。尽管数据很适合分子场计算，但是否可以将这种分子场近似应用于其他CMR镧锰矿仍是一个悬而未决的问题。我们打算对阳离子掺杂的镧锰铁矿进行全面而系统的研究，并将从这些材料获得的电阻率和磁化强度与分子场计算进行比较。我们选择的材料是碱金属和碱土金属掺杂的镧锰酸盐La 1-x A x MnO 3 ，其中x = 1 / A = Ca，Sr和Ba时为3；对于A = Na，K，Rb和Cs，x = 1/6。我们以此方式研究的所有材料的空穴掺杂水平均相同。它还避免了诸如La 1-xy Y y Ca x MnO 3 等多阳离子掺杂引起的复杂性。子>。由于难以生长掺杂碱金属的镧锰矿，我们选择制造薄膜来代替。薄膜是通过电子束/热共蒸发法制造的，已证明适用于这些材料。在所有CMR锰矿薄膜中，磁化强度随温度 M （T）的变化与分子场计算非常吻合，但电阻率随温度ρ（T）的变化无法用理论来解释。第5章给出了简单的解释。

著录项

  • 作者

    Chen, Chun-Che.;

  • 作者单位

    The University of Texas at Austin.;

  • 授予单位 The University of Texas at Austin.;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 1999
  • 页码 95 p.
  • 总页数 95
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 O49;
  • 关键词

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