Long-Range Antiferromagnetic Ordering in B‑Site Ordered Double Perovskite Ca₂ScOsO₆

A new Os-based B-site ordered double perovskite with the chemical composition of Ca2ScOsO6 was successfully synthesized. The crystal structure of the title compound was determined by employing the powder X-ray diffraction method and was found to crystallize in the monoclinic P21/n space group with the cell constants of a = 5.4716(1) Å, b = 5.6165(1) Å, c = 7.8168 (1) Å, and β = 89.889 (2)°. The temperature-dependent magnetic susceptibility data suggest that this novel S = 3/2 compound undergoes an antiferromagnetic transition at ∼69 K. Fitting the high-temperature susceptibility data (100–300 K) to Currie–Weisse behavior showed C = 1.734 emu·K/mol (μeff = 3.72 bohr magnetons) and θ = −341 K, which is indicative of dominant antiferromagnetic interactions. Temperature-dependent specific heat measurements exhibit a λ shape anomaly at 69 K, which is consistent with a long-range ordering of the spins. Because of a triangular arrangement of antiferromagnetically ordered magnetic ions, the system exhibits some degree of geometric magnetic frustration (GMF), but not strongly. Spin-dimer analysis, employing extended Hückel theory, reveals that a dominant exchange interaction exists (along the a crystallographic axis in perovskite layer), which violates the perfect condition for GMF.本研究成功合成了一种基于锇（Os）的B位有序双钙钛矿（double perovskite）材料，其化学组成为Ca₂ScOsO₆。通过粉末X射线衍射（powder X-ray diffraction）方法解析了该目标化合物的晶体结构，结果表明其结晶于单斜晶系P2₁/n空间群，晶胞参数为a=5.4716(1) Å，b=5.6165(1) Å，c=7.8168(1) Å，β=89.889(2)°。变温磁化率测试结果显示，这种自旋量子数S=3/2的新型化合物在约69 K处发生反铁磁相变。将100~300 K温区的高温磁化率数据拟合至居里-外斯（Curie-Weiss）模型，得到居里常数C=1.734 emu·K/mol（有效磁矩μeff=3.72玻尔磁子（Bohr magneton））以及θ=-341 K，这表明体系中存在主导性的反铁磁相互作用。变温热容测试在69 K处呈现λ型反常峰，与自旋长程有序的相变结果一致。由于反铁磁有序的磁离子呈三角排布，该体系表现出一定程度的几何磁阻挫（geometric magnetic frustration, GMF），但阻挫强度并不显著。采用扩展休克尔（extended Hückel）理论开展自旋二聚体分析后发现，体系中存在主导性的交换相互作用（沿钙钛矿层内的晶轴a方向），该相互作用破坏了几何磁阻挫所需的完美条件。