Remnant magnetization above room temperature in the semiconductor Y_0.5Ca_0.5BaCo₄O₇

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• 作者：Martin Valldor
• 关键词：Magnetic disorder ; Semiconductor ; Magnetic relaxation ; Cobaltate ; Rietveld
• 刊名：Solid State Sciences
• 出版年：2006
• 出版时间：November 2006
• 年：2006
• 卷：8
• 期：11
• 页码：1272-1280
• 全文大小：554 K

文摘

The Y_0.5Ca_0.5BaCo₄O₇ compound exhibits four magnetic anomalies at the temperatures 387, 281, 52, and 14 K; all anomalies show characteristics typical for spin freezing into disordered states: frequency dependent transition temperature in the AC magnetic susceptibility together with relaxation of thermoremnant magnetization. Y_0.5Ca_0.5BaCo₄O₇ is a semiconductor with a small band-gap of 0.17 eV concluded from four-point conductivity measurements and the conductivity is proportional to T^−3/4, suggesting an electron hopping mechanism involving Co²⁺ and Co³⁺ ions; at higher temperatures, double-exchange is the proposed reason for the strong magnetic interaction. At lower temperatures, super-exchange interactions start to compete with the double-exchange for domination and this competition together with geometrical frustrations in the structure are responsible for magnetic disorder down to 2 K. Covalence between Co and O is also discussed as additional reason for the strong magnetic interactions.