Abstract

This paper presents structural, magnetic, and electrical characteristics of manganites in the system \({\text{La}}_{{0.7}}^{{3 + }}{\text{Sr}}_{{{\text{0}}{\text{.3}}}}^{{{\text{2 + }}}}{\text{Mn}}_{{0.6\, - \,x\, - \,2\gamma }}^{{3 + }}{\text{Mn}}_{{0.3\, + \,x\, + \,2\gamma }}^{{4 + }}{\text{Fe}}_{{0.1\, - \,x}}^{{3 + }}{\text{Mg}}_{x}^{{2 + }}{\text{O}}_{{3\, + \,\gamma }}^{{2 - }}\) (0 ≤ x ≤ 0.1) synthesized by solid-state reactions. Sintering was performed in air at 1423 K. Samples with stoichiometric oxygen content (γ = 0) were obtained by annealing at 1223 K and partial oxygen pressure of 0.1 Pa. All studied manganites have rhombohedral structure. With an increase in magnesium content, the unit cell volume decreases, and annealed samples have a larger cell volume than the initial (sintered) manganites containing over-stoichiometric oxygen. The ratio of lattice parameters c/a is practically unchanged. Curie point of manganites decreases in general with an increase in magnesium content, showing weakly expressed plateau in the region of 0.025 < x < 0.075. Magnetization and “metal–semiconductor” transition temperature have maximum values at x = 0, then change non-monotonically, and at x > 0.075 fall sharply. Manganite, which contains the largest amount of magnesium, has the highest resistance at temperatures below 180 K and is characterized by the largest width of the temperature interval of “ferromagnetic–paramagnetic” transition, which indicates the existence of magnetic inhomogeneities. Electromagnetic parameters of initial and annealed samples differ slightly. A number of effects and competing factors that determine complicated dependencies of electromagnetic characteristics of manganites in this system on the composition are considered: inhomogeneous distribution of Mg²⁺ and Fe³⁺ ions; increased concentration of Mn⁴⁺ ions and their shielding by magnesium ions; violation of double exchange interaction between Mn⁴⁺ and Mn³⁺ by ions replacing manganese; difference in magnetic moments of the latter; changes in characteristics of magnetic inhomogeneities.

中文翻译：

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La 0.7 Sr 0.3 Mn 0.9 Fe 0.1 – x Mg x O 3 +γ锰矿八面体亚晶格中锰离子环境对其性能的影响

摘要

本文介绍了系统\（{\ text {La}} _ {{0.7}} ^ {{3+}} {\ text {Sr}} _ {{{\ text {0}} {\ text {.3}}}} ^ {{{\ text {2 +}}}}} {\ text {Mn}} _ {{0.6 \，-\，x \，-\，2 \ gamma}} ^ {{{3 +}} {\ text {Mn}} _ {{0.3 \，+ \，x \，+ \，2 \ gamma}} ^ {{4 +}} {\ text {Fe }} _ {{0.1 \，-\，x}} ^ {{3 +}} {\ text {Mg}} _ {x} ^ {{2 +}} {\ text {O}} __ {{3 \，+ \，\ gamma}} ^ {{2-}} \）（0≤x≤0.1）通过固态反应合成。在空气中以1423 K进行烧结。通过在1223 K退火和部分氧压为0.1 Pa的条件下获得的化学计量氧含量（γ= 0）的样品。所有研究的锰铁矿均具有菱面体结构。随着镁含量的增加，晶胞体积减小，并且退火后的样品的晶胞体积比含有过量化学计量氧的初始（烧结）锰矿更大。晶格参数c / a的比率实际上没有变化。锰的居里点通常随着镁含量的增加而降低，在0.025 < x <0.075的区域内表现出弱表达的平稳期。磁化强度和“金属-半导体”转变温度的最大值为x = 0，然后非单调更改，并且在x > 0.075处急剧下降。锰含量最高的镁，在低于180 K的温度下具有最高的电阻，其特征是“铁磁-顺磁”转变的温度区间最大，这表明存在磁不均匀性。初始和退火样品的电磁参数略有不同。考虑了许多影响和竞争因素，这些因素决定了该系统中锰矿的电磁特性对组成的复杂依赖性：Mg ²⁺和Fe ³⁺离子的不均匀分布；Mn ^4+的浓度增加离子及其被镁离子屏蔽；离子替代锰违反了Mn ⁴⁺和Mn ³⁺之间的双重交换相互作用；后者的磁矩差；磁不均匀特性的变化。