Abstract The pyrochlore, Gd2FeSbO7, having general formula unit A2B2O7, was chosen for magnetic and heat capacity study in this work due to presence of Fe3+ moments, whose 3d orbitals (3d5: 3 t 2 g 3 e g 2 ) are half-filled and carry a large magnetic moment, at B site of the structure, and hence create additional Gd−O−Fe−O−Gd pathways, which result in strongly antiferromagnetic superexchange interactions among the Gd−Gd spins as well as for the Gd−Fe bonds. Gd2FeSbO7 behaves paramagnetic down to ~10 K with effective antiferromagnetic nearest-neighbour interactions resulting negative Curie-Weiss temperature, θCW = −12.62 K. Fe sublattice exhibits a weak ferromagnetic transition at TC ≈ 5 K. The frustration index f = |θCW|/TC becomes 2.5 indicative of moderate frustration, which may prevent Palmer-Chalker ground state configuration of Gd sublattice at lower temperature in the system. Heat capacity Cp exhibits a broad anomaly at ~3.1 K and calculated magnetic heat capacity Cm/T attains a peak at ~1 K, but is much weaker than for other pyrochlores Gd2B2O7 (B = Sn, Ti, Ge, Pt) which are all found to order at 1 K or lower, thereby reflecting a short-range second-order transition in Gd2FeSbO7. The nature of transition was also verified by Arrott plot of magnetization. Finally the magneto-thermodynamic data were analyzed on the basis of a cooperative two-sublattice model taking account of intra-sublattice (Gd−Gd and Fe−Fe) and inter-sublattice (Gd−Fe) magnetic interactions, defined by three molecular-field parameters, λGd−Gd = −0.71 T/μB, λFe−Fe = 0.87 T/μB, and λGd−Fe = −0.61 T/μB in presence of the easy-planer crystal-field anisotropy at Gd-site. Without Gd−Fe interaction, two independent interpenetrating Gd3+ and Fe3+Sb5+ sublattices can not precisely demonstrate the measured thermomagnetic properties of Gd2FeSbO7. This study thus revealed that 3d−4f magnetic interactions offer Gd2FeSbO7 a unique place in the series of gadolinium-based pyrochlores.

中文翻译：

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合作二亚晶格分子场模型中挫败烧绿石Gd2FeSbO7的磁热力学性质

摘要 烧绿石 Gd2FeSbO7 具有通式单元 A2B2O7，由于存在 Fe3+ 矩，其 3d 轨道 (3d5: 3 t 2 g 3 eg 2 ) 是半填充的，因此在这项工作中选择用于磁和热容量研究在结构的 B 位点有一个大磁矩，因此产生额外的 Gd-O-Fe-O-Gd 通路，导致 Gd-Gd 自旋和 Gd-Fe 键之间强烈的反铁磁超交换相互作用。Gd2FeSbO7 顺磁性低至~10 K，有效的反铁磁最近邻相互作用导致负居里-魏斯温度，θCW = -12.62 K。Fe 亚晶格在 TC ≈ 5 K 处表现出弱铁磁转变。挫败指数 f = |θCW|/ TC 变为 2.5，表示中度挫折，这可能会阻止系统中较低温度下 Gd 亚晶格的 Palmer-Chalker 基态构型。热容 Cp 在 ~3.1 K 处表现出广泛的异常，计算出的磁热容 Cm/T 在 ~1 K 处达到峰值，但比其他烧绿石 Gd2B2O7（B = Sn、Ti、Ge、Pt）弱得多，它们都是发现在 1 K 或更低处有序，从而反映了 Gd2FeSbO7 中的短程二阶跃迁。转变的性质也通过磁化的阿罗特图来验证。最后，在考虑亚晶格内（Gd-Gd 和 Fe-Fe）和亚晶格间 (Gd-Fe) 磁相互作用的合作二亚晶格模型的基础上分析了磁热力学数据，由三个分子定义场参数，λGd-Gd = -0.71 T/μB，λFe-Fe = 0.87 T/μB，λGd-Fe = -0。在 Gd 位点存在易平面晶体场各向异性时为 61 T/μB。没有 Gd-Fe 相互作用，两个独立的互穿 Gd3+ 和 Fe3+Sb5+ 亚晶格不能精确地证明 Gd2FeSbO7 的热磁特性。因此，这项研究揭示了 3d-4f 磁相互作用为 Gd2FeSbO7 提供了一系列钆基烧绿石中的独特位置。