Structural studies and magnetic and transport properties of Cr-substituted La0.67Ba0.33Mn1−xCrxO3 (0 ≤ x ≤ 0.15) perovskites

We have investigated the structural, magnetic and electrical transport properties of a series of ABO3-type perovskite compounds, La0.67Ba0.33Mn1−xCrxO3 (0 ≤ x ≤ 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 ≤ 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 Tc and the magnetization M when x increases (x ≤ 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 ≤ 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 ρ = ρ0 + ρ2T2 + ρ4.5T4.5, 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 eg (↑) electron due to the substitution of Mn3+ by Cr3+, which suppresses the double exchange (DE) interactions.

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► Successive substitution of Cr at Mn site in La0.67Ba0.33Mn1−xCrxO3 manganites makes both the Curie temperature Tc and the magnetization M to diminish.
► The Cr-doped manganites La0.67Ba0.33Mn1−xCrxO3 present a single magnetic transition from ferromagnetic to paramagnetic phase.
► The La0.67Ba0.33Mn1−xCrxO3 (x ≤ 0.1) have a metallic behavior in the whole temperature range, while La0.67Ba0.33Mn0.85Cr0.15O3 remains semiconducting.
► The structure for La0.67Ba0.33Mn1−xCrxO3 (x ≤ 0.1) is rombohedral, while for x = 0.15 the structure becomes cubic.