Abstract The crucial role of high Bi-content on magnetic properties of ambient pressure synthesized double perovskite La2−xBixMnCoO6 (x = 0, 0.5 and 1) has been investigated. Structural characterization was carried out using X-ray and electron diffraction analyses as well as HAADF-STEM imaging, which confirm the monoclinic structure with P21/n space group for all compositions. A comprehensive dc-magnetization and ac-susceptibility studies unravel the complex magnetic features of parent La2MnCoO6 and its associated changes upon substitution of La by Bi. Both the ferromagnetic TC and reduced magnetization with increase in Bi-content, originated from weakening of ordered Mn4+—O—Co2+ superexchange interactions. Bi-substitution also leads to suppression in magnetic disordering, which should strengthen the ferromagnetic state. These antagonist effects i.e. suppression of disordering and lowering of TC can be related to the evolution of Mn3+—O—Co3+ (e1—O—e1) vibronic ferromagnetism of smaller exchange stabilization. The local lattice distortion due to stereoactive 6s2-electron pairs of Bi3+ possibly results in cooperative lattice distortion favouring the stabilization of Jahn-Teller active intermediate-spin state Co3+ and high spin Mn3+. It is suggested that Bi-substitution favours the reaction Co2+ + Mn4+ = Co3+ + Mn3+ to the right side, which is otherwise biased to left by 0.2 eV.

中文翻译：

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阐明 Bi 取代对 La2−xBixMnCoO6 (x = 0, 0.5 和 1) 中振动铁磁性的作用

摘要 研究了高铋含量对常压合成双钙钛矿 La2−xBixMnCoO6 (x = 0、0.5 和 1) 磁性能的关键作用。使用 X 射线和电子衍射分析以及 HAADF-STEM 成像进行结构表征，这证实了所有成分的 P21/n 空间群的单斜结构。一项全面的直流磁化和交流磁化率研究揭示了母体 La2MnCoO6 的复杂磁性特征及其在用 Bi 取代 La 后的相关变化。铁磁性 TC 和随着 Bi 含量增加而降低的磁化强度均源于有序 Mn4+-O-Co2+ 超交换相互作用的减弱。双取代还导致磁无序的抑制，这应该会加强铁磁状态。这些拮抗作用 i．e. 抑制无序和降低 TC 可能与较小交换稳定的 Mn3+-O-Co3+ (e1-O-e1) 振动铁磁性的演变有关。由于 Bi3+ 的立体活性 6s2-电子对导致的局部晶格畸变可能导致协同晶格畸变，有利于 Jahn-Teller 活性中间自旋态 Co3+ 和高自旋 Mn3+ 的稳定。表明 Bi 取代有利于反应 Co2+ + Mn4+ = Co3+ + Mn3+ 向右，否则向左偏向 0.2 eV。由于 Bi3+ 的立体活性 6s2-电子对导致的局部晶格畸变可能导致协同晶格畸变，有利于 Jahn-Teller 活性中间自旋态 Co3+ 和高自旋 Mn3+ 的稳定。表明 Bi 取代有利于反应 Co2+ + Mn4+ = Co3+ + Mn3+ 向右，否则向左偏向 0.2 eV。由于 Bi3+ 的立体活性 6s2-电子对导致的局部晶格畸变可能导致协同晶格畸变，有利于 Jahn-Teller 活性中间自旋态 Co3+ 和高自旋 Mn3+ 的稳定。表明 Bi 取代有利于反应 Co2+ + Mn4+ = Co3+ + Mn3+ 向右，否则向左偏向 0.2 eV。