Effect of Iron Doping on Structural, Magnetic, and Electrical Characteristics of Manganites in La_(0.7)Sr_(0.3)Mn_(0.9)Zn_(0.1-x)Fe_xO_3 (0≤x≤0.1) System

摘要

Experimental data on the structure and properties of manganites of La_(0.7)Sr_(0.3)Mn_(0.9)Zn_(1-x)Fe_xO_3 (0≤ ⅹ ≤ 0.1) system synthesized by ceramic processing and annealed under conditions ensuring the achievement of stoi-chiometric oxygen concentrations are presented. All obtained manganites have a rhombohedral structure. The substitution of iron for zinc leads to an increase in the unit cell volume and average cation-anion distance in the octahedral sublattice, which is determined by the increase in the concentration of Mn~(3+) ions due to the decrease in the concentration of Mn~(4+) as a result of charge compensation processes. The angles between the Mn-O-Mn bonds change slightly. Curie point, magnetization, and temperature of the metal-semiconductor transition as a function of the concentration of iron are characterized by the presence of a maximum. The maximum value of the resistance of manganite with ⅹ = 0.1 is a factor of 800-1000 higher than the maximum values of the resistance of other samples in the studied range of temperatures. Temperature dependences of magnetic permeability are indicative of the existence of magnetic inhomogeneities in manganites, especially in the samples with ⅹ = 0 and 0.1, which may be due to the nonuniform distribution of Zn~(2+) ions and the presence of ferromagnetic and paramagnetic clusters. These data are in agreement with the results of the investigation of the electron paramagnetic resonance (EPR) spectra containing additional and/or broadened lines. Characteristic features of the dependences of the properties of studied manganites on the concentration of iron are explained by the influence of a series of competing factors, namely, the decrease in the concentration of Mn~(4+) ions and probability of antiferromagnetic interaction between them, change in the number of disturbed exchange bonds between Mn~(4+) and Mn~(3+) ions, and variations of the characteristics of magnetic inhomogeneities.