双延龄草晶格反铁磁体KBaCr$_2$(PO$_4$)$_3$的基态性质
Ground-state properties of the double trillium lattice antiferromagnet KBaCr$_2$(PO$_4$)$_3$
AI总结：
该研究通过多种实验测量结合密度泛函计算，表征了双延龄草晶格材料KBaCr$_2$(PO$_4$)$_3$的结构与磁性质，揭示其两级磁相变特征及自旋晶格耦合消除阻挫的机制。
摘要：
由共角三角形单元构成的延龄草晶格是三维磁阻挫的研究平台。本文结合密度泛函能带计算，通过X射线衍射、磁化率、热容、热导率以及$^{31}$P核磁共振（NMR）测量，报道了铬基双延龄草晶格材料KBaCr$_2$(PO$_4$)$_3$的结构与磁性质。热容和$^{31}$P NMR测量显示，零场下该材料在$T_{\rm N1} \backsimeq 13.5$ K处发生磁相变，弱外加场下在$T_{\rm N2} \backsimeq 7$ K处发生另一相变。NMR亚晶格磁化结果证实$T_{\rm N1}$处的相变具有三维本质。有序态下的$^{31}$P自旋-晶格弛豫率遵循$T^3$行为，表明存在双磁振子拉曼过程。KBaCr$_2$(PO$_4$)$_3$的自旋晶格包含两个晶体学上不等价的铁磁亚晶格，二者以反铁磁方式耦合，从而消除了该延龄草网络中的阻挫。
英文摘要：
Trillium lattices formed by corner-shared triangular units are the platform for magnetic frustration in three dimensions. Herein, we report structural and magnetic properties of the Cr-based double trillium lattice material KBaCr$_2$(PO$_4$)$_3$ studied by x-ray diffraction, magnetization, heat capacity, thermal conductivity, and $^{31}$P nuclear magnetic resonance (NMR) measurements complemented by density-functional band-structure calculations. Heat capacity and $^{31}$P NMR measurements reveal the magnetic transition at $T_{\rm N1} \simeq 13.5$ K in zero field followed by another transition at $T_{\rm N2} \simeq 7$ K in weak applied fields. The NMR sublattice magnetization confirms that the transition at $T_{\rm N1}$ is 3D in nature. The $^{31}$P spin-lattice relaxation rate in the ordered state follows the $T^3$ behavior indicative of the two-magnon Raman process. The spin lattice of KBaCr$_2$(PO$_4$)$_3$ comprises two crystallographically nonequivalent ferromagnetic sublattices that are coupled antiferromagnetically, thus eliminating frustration in this trillium network.
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