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arXiv 1407.7813cond-mat.mtrl-sci
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Cu的准二维$S=1/2$磁性[C $_6$ H $_2$(COO)$_4$ ][C $_2$ H $_5$ NH $_3$ ] $_2$

Quasi-two-dimensional $S=1/2$ magnetism of Cu[C$_6$H$_2$(COO)$_4$][C$_2$H$_5$NH$_3$]$_2$

R. Nath, M. Padmanabhan, S. Baby, A. Thirumurugan, D. Ehlers, M. Hemmida, H. -A. Krug von Nidda, A. A. Tsirlin

摘要:

我们报告的结构和磁性的自旋$\frac12$量子反铁磁体Cu[C $_6$ H $_2$(COO)$_4$ ][C $_2$ H $_5$ NH $_3$ ] $_2$通过单晶X射线衍射,磁化强度,热容,和电子自旋共振(ESR)测量多晶样品,以及能带结构计算。该化合物的三斜晶系晶体结构特征为CuO $_4$片晶单元通过均苯四甲酸的阴离子[C $_6$ H $_2$(COO)$_4$ ] $^{4-}$连接成二维骨架。乙胺阳离子[C $_2$ H $_5$ NH $_3]^+$]位于层之间并充当间隔物。磁化率和热容量测量建立了准二维的,弱各向异性和非阻挫自旋$\frac12$正方形晶格与耦合的比例$J_a/J_c\simeq 0.7$沿$a$和$c$方向,分别。在1.8K以下的热力学测量中没有发现明显的长程磁序特征。然而,ESR谱线的逐渐变宽表明磁有序发生在较低的温度下。领先的磁耦合介导的有机阴离子的均苯四甲酸,并表现出一个非平凡的依赖Cu-Cu距离,与更强的耦合之间的那些Cu原子,进一步分开。

英文摘要:

We report structural and magnetic properties of the spin-$\frac12$ quantum antiferromagnet Cu[C$_6$H$_2$(COO)$_4$][C$_2$H$_5$NH$_3$]$_2$ by means of single-crystal x-ray diffraction, magnetization, heat capacity, and electron spin resonance (ESR) measurements on polycrystalline samples, as well as band-structure calculations. The triclinic crystal structure of this compound features CuO$_4$ plaquette units connected into a two-dimensional framework through anions of the pyromellitic acid [C$_6$H$_2$(COO)$_4$]$^{4-}$. The ethylamine cations [C$_2$H$_5$NH$_3]^+$ are located between the layers and act as spacers. Magnetic susceptibility and heat capacity measurements establish a quasi-two-dimensional, weakly anisotropic and non-frustrated spin-$\frac12$ square lattice with the ratio of the couplings $J_a/J_c\simeq 0.7$ along the $a$ and $c$ directions, respectively. No clear signatures of the long-range magnetic order are seen in thermodynamic measurements down to 1.8\,K. However, the gradual broadening of the ESR line suggests that magnetic ordering occurs at lower temperatures. Leading magnetic couplings are mediated by the organic anion of the pyromellitic acid and exhibit a non-trivial dependence on the Cu--Cu distance, with the stronger coupling between those Cu atoms that are further apart.

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