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arXiv · 0801.4188

Magnetic and structural transitions in La$_{1-x}A_{1-x}$CoO$_{3}$ ($A$ = Ca, Sr, and Ba)

M. Kriener·M. Braden·H. Kierspel·D. Senff·O. Zabara·C. Zobel·T. Lorenz
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Abstract

We report thermal-expansion, lattice-constant, and specific-heat data of the series La_1-xA_xCoO_3 for 0<= x <= 0.30 with A = Ca, Sr, and Ba. For the undoped compound LaCoO_3 the thermal-expansion coefficient alpha(T) exhibits a pronounced maximum around T=50K caused by a temperature-driven spin-state transition from a low-spin state of the Co^{3+$ ions at low towards a higher spin state at higher temperatures. The partial substitution of the La^{3+} ions by divalent Ca^{2+}, Sr^{2+}, or Ba^{2+} ions causes drastic changes in the macroscopic properties of LaCoO3. The large maximum in alpha(T) is suppressed and completely vanishes for x> 0.12. For A = Ca three different anomalies develop in alpha(T) with further increasing x, which are visible in specific-heat data as well. Together with temperature-dependent x-ray data we identify several phase transitions as a function of the doping concentration x and temperature. From these data we propose an extended phase diagram for La_1-xCa_xCoO_3.

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M. Kriener, M. Braden, H. Kierspel, D. Senff, O. Zabara, C. Zobel, T. Lorenz. 2008-01-28. Magnetic and structural transitions in La$_{1-x}A_{1-x}$CoO$_{3}$ ($A$ = Ca, Sr, and Ba). https://doi.org/10.1103/physrevb.79.224104

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