Charge trapping in optimally doped epitaxial manganite thin films
Charge trapping in optimally doped epitaxial manganite thin films
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DOI：
10.1103/physrevb.66.134416
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发表时间：
2002-10
影响因子：
3.7
通讯作者：
M. Bibes;S. Valencia;L. Balcells;B. Martínez;J. Fontcuberta;M. Wójcik;S. Nadolski;E. Jedryka
中科院分区：
文献类型：
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作者：
M. Bibes;S. Valencia;L. Balcells;B. Martínez;J. Fontcuberta;M. Wójcik;S. Nadolski;E. Jedryka
研究了在单晶衬底上外延生长的La2/3Ca1/3MnO3薄膜的磁输运特性与厚度的关系。随着厚度的减小，薄膜的磁电性能发生了全面的破坏，即电阻率和低温磁阻增大，金属-绝缘体的转变温度(Tp)降低。我们指出，这些薄膜的电学性质，特别是靠近薄膜/衬底界面的电学性质，与块体材料的不同。核磁共振测量证实了这一点，这些测量提供了证据，表明这些薄膜具有不均匀的磁电纳米结构，具有包含局域电荷的可区分区域。这些区域分散在薄膜内部，在SrTiO3衬底上生长的La2/3Ca1/3MnO3薄膜具有较高的密度，而在NdGaO3衬底上生长的La2/3Ca1/3MnO3薄膜的密度分布更均匀。由于我们的锰氧化物薄膜具有几乎不松弛的晶体结构，Tp的厚度依赖关系既不与应变态有关，也不与尺寸效应有关。或者，我们发现不同电子相的共存导致了金属区域载流子密度的改变，并可能导致了Mn-O键长和Mn-O-Mn角的无序性的增强。我们认为，这两个因素的共同作用促进了双交换传递积分的降低，从而解释了最薄薄膜的居里温度降低的原因。根据锰氧化物与绝缘性钙钛矿界面的微观结构，讨论了造成这种相分离的可能机制。
We have studied the thickness dependence of the magnetotransport properties of La 2 / 3 Ca 1 / 3 MnO 3 thin films epitaxially grown on SrTiO 3 , LaAlO 3 , and NdGaO 3 single-crystalline substrates. When thickness decreases, aglobal disruption of the magnetoelectronic properties occurs, namely the resistivity and the low-temperature magnetoresistance increase while the metal-to-insulator transition temperature (Tp) is lowered. We state that the electronic properties of these films, especially close to the film/substrate interface, differ from those of the bulk material. This is confirmed by nuclear-magnetic-resonance measurements which provide evidence that these films have an inhomogeneous magnetoelectronic nanostructure with distinguishable regions containing localized charges. These regions are scattered within the films, with a higher density close to interfaces in the case of La 2 / 3 Ca 1 / 3 MnO 3 films on SrTiO 3 but more homogeneously distributed for films grown on NdGaO 3 . Since our manganite films have a virtually unrelaxed crystal structure, the thickness dependence of Tp can neither be related to the strain states nor to dimensional effects. Alternatively, we show that the coexistence of different electronic phases leads to a modification of the carrier density in the metallic regions and, presumably, to an enhancement of the disorder in the Mn-O bond length and Mn-O-Mn angles. We will argue that the conjunction of both factors promotes a decrease of the double exchange transfer integral and, consequently, accounts for the reduction of the Curie temperature for the thinnest films. The possible mechanisms responsible for this phase separation are discussed in terms of the microstructure of the interfaces between the manganite and the insulating perovskite.