A. V. Pashchenko, V. P. Pashchenko, A. G. Silcheva, V. K. Prokopenko, A. A. Shemyakov, Yu. F. Revenko, V. P. Komarov, S. V. Gorban', “Structure, phase transitions, $^{55}$Mn NMR, and magnetoresistive properties of La$_{0.6}$Sr$_{0.2}$Mn$_{1.2-y}$Cr$_y$O$_{3\pm\delta}$”, Fizika Tverdogo Tela, 2011, Volume 53, Issue 2,Pages 289

This article is cited in 4 papers

Magnetism

Structure, phase transitions, $^{55}$Mn NMR, and magnetoresistive properties of La$_{0.6}$Sr$_{0.2}$Mn$_{1.2-y}$Cr$_y$O$_{3\pm\delta}$

A. V. Pashchenko^ab, V. P. Pashchenko^ac, A. G. Silcheva^d, V. K. Prokopenko^a, A. A. Shemyakov^a, Yu. F. Revenko^a, V. P. Komarov^c, S. V. Gorban'^b

^a Galkin Donetsk Institute for Physics and Engineering, Donetsk
^b Donetsk National University of Economics and Trade named after M. I. Tugan-Baranovsky, Donetsk
^c Research Institute "Reactivelectron"
^d Lugansk Taras Shevchenko National University

Abstract: The structure and properties of lanthanum strontium manganite perovskites La$_{0.6}$Sr$_{0.2}$Mn$_{1.2-y}$Cr$_y$O$_{3\pm\delta}$ ($y$ = 0 – 0.3) sintered at 1430$^\circ$C have been studied by X-ray, resistive, and magnetic ($\chi_{\mathrm{ac}}$ and $^{55}$Mn NMR) methods. The parameter of the rhombohedrally distorted $(R\bar3c)$ perovskite structure decreases with increasing $y$. The real perovskite structure contains point (anion and cation vacancies) and cluster-type nanostructure defects. The analysis of asymmetrically broadened $^{55}$Mn NMR spectra has confirmed the high-frequency electron-hole exchange Mn$^{3+}$ $\leftrightarrow$ Mn$^{4+}$ and local inhomogeneity of their surrounding by other ions and point and cluster-type defects. An increase in the Cr content leads to an increase in the resistivity and the magnetoresistive effect and a decrease in the metal-semiconductor and ferromagnetic-paramagnetic phase transition temperatures ($T_{ms}$ and $T_c$) due to the distortion of the exchange interactions Mn$^{3+}$ $\leftrightarrow$ Mn$^{4+}$ by chromium ions, vacancies, and clusters. Introduction of Cr decreases the ferromagnetic component and increases the activation energy. The magnetoresistive effect near $T_{ms}$ and $T_c$ is caused by scattering of charge carriers from intercrystallite nanostructure inhomogeneities of the lattice, and the low-temperature effect is associated with the tunneling on mesostructural intercrystallite boundaries.

Received: 22.04.2010