Intrinsic electrical transport and magnetic properties of La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3 MOCVD thin films and bulk material
Intrinsic electrical transport and magnetic properties of La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3 MOCVD thin films and bulk material
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DOI：
10.1103/physrevb.53.14434
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发表时间：
1996-06-01
影响因子：
3.7
通讯作者：
Geballe, TH
中科院分区：
文献类型：
--
作者：
Snyder, GJ;Hiskes, R;Geballe, TH
通过比较块状样品与薄膜的行为，完成了旨在显示钙钛矿亚锰酸盐固有特性的研究。通过固源化学气相沉积在 LaAlO3 上生长钙钛矿 La0.67Ca0.33MnO3 和 La0.67Sr0.33MnO3 的外延 1500 埃薄膜，并在 950 摄氏度的氧气中进行后退火。通过激光加热基座生长制备晶体。多晶颗粒、晶体的磁和电传输特性 和退火膜本质上是一样的。低于 T-C/2 时，固有磁化强度随着 T-2 的增加而降低（正如对于流动电子铁磁体所预期的那样），而固有电阻率则与 T-2 成比例地增加。电阻率常数和 T-2 系数很大程度上与磁场和碱土元素（Ca、Sr 或 Ba）无关。霍尔效应测量表明空穴是金属态的移动载流子。我们确定了三种不同类型的负磁阻。在居里温度附近观察到的最大影响是 Sr 为 25%，Ca 化合物为 250% [Delta R/R(H)]。还存在与多晶样品的净磁化强度相关的磁阻，这在薄膜中是看不到的。最后，即使在低温下，也可以观察到 H 中的小磁阻线性。 La0.67Sr0.33MnO3 的高温（高于 T-C）电阻率与小极化子跳跃电导率一致，在 750 K 时有轻微转变，而 La0.67Sr0.33MnO3 直到约 500 K 才表现出激活的电导率，远高于 T-C。有限的低温和高温电阻率限制了这些材料的最大可能磁阻，并且可以解释为什么文献中报道的“巨大”磁阻与 T-C 的抑制相关。
An investigation designed to display the intrinsic properties of perovskite manganites was accomplished by comparing the behavior of bulk samples with that of thin films. Epitaxial 1500 Angstrom films of perovskite La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3 were grown by solid source chemical vapor deposition on LaAlO3 and post annealed in oxygen at 950 degrees C. Crystals were prepared by laser heated pedestal growth, The magnetic and electrical transport properties of the polycrystalline pellets, crystals, and annealed films are essentially the same. Below T-C/2 the intrinsic magnetization decreases as T-2 (as can be expected for itinerant electron ferromagnets) while the intrinsic resistivity increases proportional to T-2. The constant and T-2 coefficients of the resistivity are largely independent of magnetic field and alkaline earth element (Ca, Sr, or Ba). Hall effect measurements indicate that holes are mobile carriers in the metallic state. We identify three distinct types of negative magnetoresistance. The largest effect, observed near the Curie temperature, is 25% for the Sr and 250% [Delta R/R(H)] for the Ca compound. There is also magnetoresistance associated with the net magnetization of polycrystalline samples which is not seen in films. Finally a small magnetoresistance linear in H is observed even at low temperatures. The high temperature (above T-C) resistivity of La0.67Sr0.33MnO3 is consistent with small polaron hopping conductivity with a slight transition at 750 K, while La0.67Sr0.33MnO3 does not exhibit activated conductivity until about 500 K, well above T-C. The limiting low and high temperature resistivities place a limit on the maximum possible magnetoresistance of these materials and may explain why the ''colossal'' magnetoresistance reported in the literature correlates with the suppression of T-C.