Structural Transitions in a La0.82Ca0.18MnO3 Single Crystal

R.I. Zainullina, N.S. Bannikova, D.A. Shulyatev
Received: 21 March 2018; Revised: 12 April 2018; Accepted: 07 May 2018
This paper is written in Russian
Citation: R.I. Zainullina, N.S. Bannikova, D.A. Shulyatev. Structural Transitions in a La0.82Ca0.18MnO3 Single Crystal. Letters on Materials, 2018, 8(3) 258-262
BibTex   DOI: 10.22226/2410-3535-2018-3-258-262

Abstract

At cooling from T~ 400 K a La0.82Ca0.18MnO3 single crystal undergoes the transition from pseudocubic O* phase to Jahn-Teller O' phase and the reverse transition from the O' to low temperature O* phase. It is surprising that low values of the internal friction are observed for crystal phase O' with significant Jahn-Teller distortions of oxygen octahedra.The influence of structural transitions from high-temperature pseudocubic O* to the Jahn−Teller O' phase and reverse transition from O' to a low-temperature O* phase on the elastic, magnetic, and transport properties of a La0.82Ca0.18MnO3 single crystal when the temperature is decreased from 400 K is studied. Significant anomalies are observed in the temperature dependences of the velocity of longitudinal sound waves and the internal friction. The sound velocity and the internal friction in the Jahn−Teller O' phase are significantly lower than those in the pseudocubic O* phase. The structural transitions take place in the temperature range 30−50 K. Majority carriers in the low-temperature O* phase are electrons, whereas majority carriers in the O' and high-temperature O* phases are holes. Electronic states are characterized by substantially stronger spin−orbit interaction than hole states. The positive magnetoresistance is observed in low magnetic fields in the low-temperature O* phase. At a certain field, the magnetoresistance changes its sign. Such magnetoresistance has not been observed in the La−Sr and La−Ba manganites. Positive magnetoresistance indicates significant anisotropy of the transport properties of the low-temperature O* phase in the La0.82Ca0.18MnO3 single crystal. It is established that the magnetic and transport properties of the low-temperature ferromagnetic O*phase differ markedly from those of the ferromagnetic Jahn—Teller O' phase.

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