Systems of Manganites with Enhanced Electromagnetic Parameters

The effects of paired substitution of 3d¹⁰ cations (\(\rm{Zn{_{0.5}^{2+}}Ge{_{0.5}^{4+}}}\)) or 2p⁶ and 3p⁶ cations (\(\rm{Mg{_{0.5}^{2+}}Ti{_{0.5}^{4+}}}\)) for manganese in polycrystalline manganites of specifically designed systems \(\text{L}{\text{a}_{0.8 - x}}\text{S}{\text{r}_{0.2 + x}}\text{Mn}_{0.8 - 2x -2\gamma}^{3 +}\text{Mn}_{0.2 + x + 2\gamma}^{4 +} \times {\left( {\text{Me}_{0.5}^{2 +}\text{Me}_{0.5}^{4 +}} \right)_x}{\text{O}_{3 + \gamma}}\) on their electromagnetic parameters are studied and compared. Temperature dependences of the resistance, magnetoresistance and magnetostriction constant are measured. In the proposed systems, the linear rise of strontium concentration simultaneously with increasing number of substituents allows high characteristics of manganites to be maintained owing to the increase in the concentration of free charge carriers, through which ferromagnetic double exchange interaction is carried out. The data obtained are also compared with the properties of Ga³⁺(3d¹⁰)-substituted manganites as peculiar standards. All sintered (Zn,Ge)-containing manganites in the temperature range from 100 to 293 K have metallic type of conductivity, while (Mg,Ti)-substituted samples exhibit semiconducting features, and Ga-containing compositions reveal a “metal-semiconductor” transition point (T_ms). The annealing under conditions ensuring stoichiometric oxygen content leads to the shift of this transition toward lower temperatures in manganites with 3d¹⁰ substituents and to the increase in T_ms in compositions with substituting p⁶ cations. In the investigated systems, the absolute values of negative magnetoresistance up to ~90–200% at 120–150 K in the field of 9.2 kOe are obtained, and the linear magnetostriction constant reaches record values of about 10^–3 in the field of 4.6 kOe. Manganite La_0.65Sr_0.35Mn_0.85Ga_0.15O₃ with a weak temperature dependence of magnetoresistance of ~20% at room temperatures is of particular service for magnetic field sensors. Possible approaches to the interpretation of established regularities demonstrating the role of electronic configurations of substituents for manganese in the formation of the properties of manganites and interesting for the development of new materials for electronics are discussed.