Structural studies and magnetic and transport properties of Cr-substituted La_0.67Ba_0.33Mn_{1鈭?span style='font-style: italic'>x}Cr_xO₃ (0 鈮?#xa0;x 鈮?#xa0;0.15) perovskites

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• 作者：Marwè ; ne Oumezzine^a ; ^b ; ^{Oumezzine@hotmail.co.uk} ; ^{marouan.omezzine@etudiant.univ-rennes1.fr} ; Octavio Pe&ntilde ; a^b ; Sami Kallel^a ; Thierry Guizouarn^b ; Mohamed Oumezzine^a
• 关键词：Mn-perovskite ; Magnetization ; Manganites ; Transport mechanism
• 刊名：Journal of Alloys and Compounds
• 出版年：2012
• 期刊代码：45_09258388
• 类别：ms
• 出版时间：25 August, 2012
• 卷：533
• 期：Complete
• 页码：33-40
• 文件大小：1130 K

摘要

We have investigated the structural, magnetic and electrical transport properties of a series of ABO₃-type perovskite compounds, La_0.67Ba_0.33Mn_1鈭?em>xCr_xO₃ (0 鈮?#xA0;x 鈮?#xA0;0.15), which strongly depend on the doping level x. The slight difference between the ionic radii of Cr³⁺ and Mn³⁺ causes no change in the structure when x 鈮?#xA0;0.1, remaining rhombohedral (space group R-3C), while for x = 0.15 the structure becomes cubic (space group Pm-3m). Energy dispersive X-ray analysis (EDAX) confirms the expected stoichiometry of all samples. Upon Cr doping on the Mn site, the lattice parameters, the unit cell volume and the BOB bond angle are reduced. All samples present a single magnetic transition from ferromagnetic to paramagnetic phase, showing a decrease of the Curie temperature T_c and the magnetization M when x increases (x 鈮?#xA0;0.15). However, Cr doping makes the saturation magnetization at 5 K to decrease, which indicates that the Cr³⁺ moments tend to be antiparallel to the Mn³⁺ moments at low temperature.

The Cr-doped manganites exhibit a large variation in resistivity values. The increase of Cr doping (x 鈮?#xA0;0.15) leads to an increase of the electrical resistivity. Below 10 at.%of Cr³⁺, the electrical resistivity shows a metallic behavior, which is well fitted by the relation 蟻 = 蟻₀ + 蟻₂T² + 蟻_4.5T^4.5, indicating the importance of the grain/domain boundary, the electron-electron scattering effects and, to a lesser extent, the electron-(magnon, phonon) scattering effects in the mechanism of conduction. On the other hand, the 15 at.%of Cr³⁺ doping makes the material to exhibit a semiconductor behavior, for which the electronic transport can be explained by a variable range hopping (VRH) and small polaron hopping (SPH) models. Results are consistent with a reduction of the number of available hopping sites for the Mn e_g (鈫? electron due to the substitution of Mn³⁺ by Cr³⁺, which suppresses the double exchange (DE) interactions.