标题： 螺旋自旋液体材料Ca$_{10}$Cr$_{7}$O$_{28}$中磁关联的两阶段演化 显示英文标题

标题： Two-stage evolution of magnetic correlations in spiral spin liquid material, Ca$_{10}$Cr$_{7}$O$_{28}$

摘要： 我们展示了一个关于单晶Ca$_{10}$Cr$_{7}$O$_{28}$的X波段可调谐高频/高场电子自旋共振（HF-ESR）研究，该材料由交替的反铁磁和铁磁kagome双层组成。 在高温下，提出了一个声子辅助弛豫过程来解释交换狭窄区域中线宽的显著增加（$k_{\rm B}T\gg J$）。 相比之下，在低温下（$k_{\rm B}T\lesssim J$），观察到线宽变窄呈幂律行为。 我们的数据揭示了线宽的两个不同的幂律区域，它们在 $T^*\approx 7.5$~K处交叉。 值得注意的是，这种具有相反符号交换相互作用的交替kagome双层系统中ESR线宽的有趣演化突显了与均匀kagome反铁磁体中不同的自旋动力学。 显示英文摘要

摘要： We present an X-band and tunable high-frequency/high-field electron spin resonance (HF-ESR) study of single-crystalline Ca$_{10}$Cr$_{7}$O$_{28}$, which constitutes alternating antiferromagnetic and ferromagnetic kagome bilayers. At high temperatures, a phonon-assisted relaxation process is evoked to account for the pronounced increase of the linewidth in an exchange-narrowing regime ($k_{\rm B}T\gg J$). In contrast, at low temperatures ($k_{\rm B}T\lesssim J$), a power-law behavior in line narrowing is observed. Our data reveal two distinct power-law regimes for the linewidth which crossover at $T^*\approx 7.5$~K. Notably, the intriguing evolution of the ESR linewidth in this alternating kagome bilayer system with opposite sign of exchange interactions highlights distinct spin dynamics compared to those in a uniform kagome antiferromagnet.