Cationic Ordering and Microstructural Effects in the Ferromagnetic Perovskite La0.5Ba0.5CoO3: Impact upon Magnetotransport Properties

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• 作者：Eeva-Leena Rautama ; Philippe Boullay ; Asish K. Kundu ; Vincent Caignaert ; Valé ; rie Pralong ; Maarit Karppinen ; Bernard Raveau
• 刊名：Chemistry of Materials
• 出版年：2008
• 出版时间：April 22, 2008
• 年：2008
• 卷：20
• 期：8
• 页码：2742 - 2750
• 全文大小：3191K
• 年卷期：v.20,no.8(April 22, 2008)
• ISSN：1520-5002

文摘

The synthesis and structural study of the stoichiometric perovskite La_0.5Ba_0.5CoO₃ have allowed three forms to be isolated. Besides the disordered La_0.5Ba_0.5CoO₃ 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° 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 T_C @ 174–179 K, but differently from the other phases, the nanoscale-ordered LaBaCo₂O₆ is a hard ferromagnet, with H_C ≈ 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 T_C 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.