Structure, phase transitions, 55Mn NMR, and magnetoresistive properties of $ La_{0.6} %$ Sr_{0.2} %$ Mn_{1.2 − y} %$ Cr_{y} %$ O_{3 ± δ} $

Abstract The structure and properties of lanthanum strontium manganite perovskites $ La_{0.6} %$ Sr_{0.2} %$ Mn_{1.2 − y} %$ Cr_{y} %$ O_{3 ± δ} $ (y = 0–0.3) sintered at 1430°C have been studied by X-ray, resistive, and magnetic ($ χ_{ac} $ and 55Mn NMR) methods. The parameter of the rhombohedrally...
Ausführliche Beschreibung

Abstract The structure and properties of lanthanum strontium manganite perovskites $ La_{0.6} %$ Sr_{0.2} %$ Mn_{1.2 − y} %$ Cr_{y} %$ O_{3 ± δ} $ (y = 0–0.3) sintered at 1430°C have been studied by X-ray, resistive, and magnetic ($ χ_{ac} $ and 55Mn NMR) methods. The parameter of the rhombohedrally distorted (R%$c) 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 55Mn NMR spectra has confirmed the high-frequency electron-hole exchange $ Mn^{3+} $ ↔ $ 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 (Tms and Tc) due to the distortion of the exchange interactions $ Mn^{3+} $ ↔ $ Mn^{4+} $ by chromium ions, vacancies, and clusters. Introduction of Cr decreases the ferromagnetic component and increases the activation energy. The magnetoresistive effect near Tms and Tc 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. Ausführliche Beschreibung