准二维自旋-1/2反铁磁体Y2CuGe4O12的磁性
Magnetic properties of a quasi-two-dimensional spin-1/2 antiferromagnet Y2CuGe4O12
AI总结：
本文通过结构表征与多种磁测量结合DFT计算，研究了Y2CuGe4O12的磁性，发现其为扭曲三角晶格磁体，近邻交换相互作用主导磁行为，为探索阻挫量子现象提供了新平台。
AI中文摘要：
空间各向异性低维磁体中，竞争型磁相互作用与阻挫诱导的量子涨落常产生包括场诱导相在内的奇异磁现象。本文对多晶Y2CuGe4O12开展晶体结构、磁化率、比热及电子自旋共振（ESR）测量，并结合密度泛函理论（DFT）计算开展研究。该化合物中，Cu²⁺离子形成扭曲三角晶格，存在面内竞争型铁磁交换相互作用（J₁≈0.138 K，J₂≈0.01 K）与反铁磁交换相互作用（J₃≈-3.22 K），以及较弱的面间反铁磁耦合（J₄≈-1.56 K），这些相互作用解释了小的居里-外斯温度θ_CW=-1.8 K。尽管反铁磁相互作用占主导，但在低至0.4 K时未观测到长程磁有序迹象，磁化率与磁比热的宽峰表明短程自旋关联的发展，低维阻挫磁体特有的临界ESR线宽展宽进一步证实了这一点。外加磁场会逐步抑制磁比热的宽峰，反映塞曼能与交换能尺度的竞争，当磁场高于饱和场μ₀H_s=2.6 T时，系统进入场极化态，此态下磁比热呈现指数温度依赖，与有能隙磁振子激发一致。这些结果确立Y₂CuGe₄O₁₂为一种罕见的扭曲三角晶格磁体，其磁行为由近邻交换相互作用主导，为探索阻挫驱动的量子现象提供了有前景的平台。
英文摘要：
Competing magnetic interactions and frustration-induced quantum fluctuations in spatially anisotropic low-dimensional magnets often give rise to exotic magnetic phenomena, including field-induced phases. Here, we present crystal structure, magnetic susceptibility, specific heat, and electron spin resonance (ESR) measurements on polycrystalline Y$2$CuGe$4$O${12}$, supported by density functional theory (DFT) calculations. In this compound, the Cu$^{2+}$ ions form a distorted triangular lattice with competing intraplanar ferromagnetic ($J_1 \approx 0.138$ K and $J_2 \approx 0.01$ K) and antiferromagnetic ($J_3 \approx -3.22$ K) exchange interactions, together with a weaker interplanar antiferromagnetic coupling ($J_4 \approx -1.56$ K). These interactions account for the small Curie--Weiss temperature, $θ{\rm CW}=-1.8$ K. Despite the dominant antiferromagnetic interactions, no signature of long-range magnetic ordering is observed down to 0.4 K. Instead, broad maxima in both the magnetic susceptibility and magnetic specific heat reveal the development of short-range spin correlations, further supported by the critical ESR linewidth broadening characteristic of low-dimensional frustrated magnets. Application of an external magnetic field progressively suppresses the broad maximum in the magnetic specific heat, reflecting competition between the Zeeman and exchange energy scales, and drives the system into a field-polarized state above the saturation field, $μ_0H_{\rm s}=2.6$ T. In this regime, the magnetic specific heat exhibits an exponential temperature dependence, consistent with gapped magnon excitations. These results establish Y$_2$CuGe$4$O${12}$ as a rare distorted triangular-lattice magnet in which further-neighbor exchange interactions dominate the magnetic behavior, providing a promising platform for exploring frustration-driven quantum phenomena.
