The colossal magnetoresistance (CMR) and metal–insulator transitions in electronically correlated manganite oxides are well-known to be driven and improved by coexisting magneto-electronic phases of competitive origin. Such magneto-electronic inhomogeneity or the so-called phase-separated state appears when several physical interactions are simultaneously active. This makes doped manganites extremely sensitive to the parameters like the nature and extent of doping, A-site cation radius (⟨𝑟𝐴⟩$⟨r_A⟩$$⟨r_A⟩$), A-site size disorder parameter (σ²) and the associated local lattice deformation, external pressure, and electric and magnetic fields. The magneto-electronic inhomogeneity is believed to play a crucial role in the emergence of CMR. The Griffiths phase magnetic inhomogeneity possesses an undecided disposition to the emergence of CMR. Here, we report investigation on electrical and magneto-electric transport properties on a series of high entropy manganite (5A_0.2)MnO₃ of fixed hole doping (40%) with the wide variation in both ⟨𝑟𝐴⟩$⟨r_A⟩$$⟨r_A⟩$ and σ². The high-entropy manganite demonstrates a system of extremely exaggerated cationic disordering. Interestingly, among the seven high entropy samples, only (La_0.2Pr_0.2Dy_0.2Sr_0.2Ba_0.2)MnO₃ exhibits Griffiths phase behavior, which ruled out the generalization of ionic size disorder-induced genesis of the Griffiths phase. The maximum CMR of −9.10 × 10³(%) is observed in the non-Griffiths phase (La_0.2Sm_0.2Eu_0.2Sr_0.2Ba_0.2)MnO₃ compared to −4.82 × 10³(%) in the (La_0.2Pr_0.2Dy_0.2Sr_0.2Ba_0.2)MnO₃ Griffiths phase. This suggests that the Griffiths phase is not a necessary precursor for the CMR effect. The magnetic state in (5A_0.2)MnO₃ is attributed to the ferromagnetic cluster formation due to the fragmented long-range exchange pathway rather than coexisting ferromagnetic and antiferromagnetic type inhomogeneity. The carrier localization in fragmented clusters plays a primordial role in the CMR effect. The ferromagnetic cluster formation critically depends on both the ⟨𝑟𝐴⟩$⟨r_A⟩$$⟨r_A⟩$ and σ². The σ² is crucial to improve MR. The observed CMR in several (5A_0.2)MnO₃ is higher than the best-known values for conventional bulk manganites. The high temperature resistivity can be better described by a variable range hopping model.

中文翻译：

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载流子定位对 Griffiths 不均匀性和相位分离对高熵锰矿磁阻的主导作用


众所周知，电子相关锰酸盐氧化物中的巨大磁阻 （CMR） 和金属-绝缘体转变是由竞争性来源的共存磁电子相驱动和改进的。这种磁电子不均匀性或所谓的相分离态出现在几个物理相互作用同时活跃时。这使得掺杂锰酸盐对掺杂的性质和程度、A 位阳离子半径 （⟨𝑟 一个⟩$⟨r_A⟩$$⟨r_A⟩$
）、A 位点尺寸无序参数 （σ ² ） 和相关的局部晶格变形、外部压力以及电场和磁场。磁电子不均匀性被认为在 CMR 的出现中起着至关重要的作用。Griffiths 相磁不均匀性对 CMR 的出现具有不确定的倾向。在这里，我们报告了对一系列固定空穴掺杂 （40%） 的高熵锰 （5A _0.2 ）MnO ₃ 的电和磁电传输特性的研究，两者的变化很大⟨𝑟 一个⟩$⟨r_A⟩$$⟨r_A⟩$
和 σ ² .高熵锰矿表现出一个极其夸张的阳离子无序系统。有趣的是，在 7 个高熵样品中，只有 （La _0.2 Pr _0.2 Dy _0.2 Sr _0.2 Ba _0.2 ）MnO ₃ 表现出 Griffiths 相行为，这排除了离子尺寸无序诱导的 Griffiths 相发生的普遍化。在非格里菲斯相 （La _0.2 Sm _0.2 Eu _0.2 Sr _0.2 Ba _0.2 ）MnO ₃ 中观察到的最大 CMR 为 -9.10 × 10 ³ （%），而在 （La _0.2 Pr _0.2 Dy _0.2 Sr _{0.2 0.2} Ba） MnO ₃ 格里菲斯相中观察到 -4.82 × 10 ³ （%）。这表明 Griffiths 相不是 CMR 效应的必要前体。（5A _0.2 ）MnO ₃ 中的磁态归因于铁磁团簇的形成，这是由于碎片化的长距离交换途径，而不是共存的铁磁和反铁磁型不均匀性。碎片化簇中的载流子定位在 CMR 效应中起着原始作用。铁磁簇的形成在很大程度上取决于⟨𝑟 一个⟩$⟨r_A⟩$$⟨r_A⟩$
和 σ ² .σ ² 对于改善 MR 至关重要。在几种 （5A _0.2 ） MnO ₃ 中观察到的 CMR 高于常规块锰矿的最已知值。高温电阻率可以用可变范围跳频模型更好地描述。