The synthesis, structural characterization and magnetic properties of the (MnR)(MnSb)O pyrochlore series are detailed herein. The R (Rare earth) and Sb cations occupy the A and B sites respectively, due to their charge/size ratio. Mn is found to be located in a 1/3 ratio in both positions with selective oxidation state due to size restrictions. Mixed valence in Mn/Mn was confirmed from EELS spectroscopy. According to their geometric frustration and R-Mn/Sb-Mn disorder, spin glass behavior is observed from and magnetic susceptibility data and no long-range magnetic order could be observed from NPD data down to 1.5 K. The magnetic entropy variation calculated from field dependent magnetization curves reveals large magnetocaloric effect (MCE) for these compounds, suggesting its relation to the dynamics of the frozen state. These values reach up to ΔS ∼20.7 J/kgK for the RGd sample, which is comparable to other materials with large MCE induced by FM order. This renders these materials competitive in magnetic refrigeration and opens the path for new enhanced magnetocaloric materials exploiting this mechanism.

中文翻译：

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(Mn1/3R2/3)2(Mn1/3Sb2/3)2O7 烧绿石系列中的自旋玻璃行为导致大磁热效应

本文详细介绍了 (MnR)(MnSb)O 烧绿石系列的合成、结构表征和磁性能。由于电荷/尺寸比，R（稀土）和 Sb 阳离子分别占据 A 和 B 位点。由于尺寸限制，Mn 被发现以 1/3 的比例位于两个具有选择性氧化态的位置。 Mn/Mn 中的混合价态通过 EELS 光谱得到证实。根据它们的几何挫败和 R-Mn/Sb-Mn 无序性，从磁化率数据中观察到自旋玻璃行为，并且从低至 1.5 K 的 NPD 数据中无法观察到长程磁序。根据场计算的磁熵变化相关磁化曲线揭示了这些化合物的大磁热效应（MCE），表明其与冷冻状态动力学的关系。对于 RGd 样品，这些值高达 ΔS ∼20.7 J/kgK，这与 FM 阶次诱导的具有大 MCE 的其他材料相当。这使得这些材料在磁制冷方面具有竞争力，并为利用这种机制的新型增强磁热材料开辟了道路。