铁磁超导体La0.5Ba 0.5CoO 3中的阳离子有序和微结构效应对磁输运性质的影响
Cationic Ordering and Microstructural Effects in the Ferromagnetic Perovskite La0.5Ba0.5CoO3: Impact upon Magnetotransport Properties
摘要：
化学计量的钙钛矿型La0.5Ba0.5CoO3的合成和结构研究允许三种形式被隔离。除了无序的La_（0.5）Ba_（0.5）CoO_3和完全有序的层状LaBaCo_2 O_6外，还得到了第三种纳米级有序的LaBaCo_2 O_6。正如透射电子显微镜调查所证明的那样，后者由112型90度取向的领域在纳米尺度上相互配合，从而诱导大的应变和局部原子尺度的晶格畸变。这三种铁磁钙钛矿表现出几乎相同的Tc（174-179 K），但与其他相不同，纳米级有序的LaBaCo 2 O 6是硬铁磁体，Hc = 4.2 kOe，这是由于可以钉扎畴壁的应变，防止自旋在磁场中反转。这些相的磁输运性质表明，它们都表现出最大的本征磁电阻，在70 kOe下在Tc附近接近6- 7%，但由于晶界效应，有序相在低温下表现出高得多的隧道磁电阻效应，约为15%对4%。
英文摘要：
The synthesis and structural study of the stoichiometric perovskite La0.5Ba0.5CoO3 have allowed three forms to be isolated. Besides the disordered La0.5Ba0.5CoO3 and the perfectly ordered layered LaBaCo2O6, a third form called nanoscale-ordered LaBaCo2O6, is obtained. As evidenced by transmission electron microscopy investigations, the latter consists of 112-type 90 degree oriented domains fitted into each other at a nanometer scale which induce large strains and consequently local atomic scale lattice distortions. These three ferromagnetic perovskites exhibit practically the same Tc (174-179 K), but differently from the other phases, the nanoscale-ordered LaBaCo2O6 is a hard ferromagnet, with Hc = 4.2 kOe, due to the strains which may pin domain walls, preventing the reversal of the spins in a magnetic field. The magnetotransport properties of these phases show that all of them exhibit a maximum intrinsic magnetoresistance, close to 6-7 % around Tc under 70 kOe but that the ordered phase exhibits a much higher tunnelling magnetoresistance effect at low temperature of about 15 % against 4 % due to the grain boundary effects.
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