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arXiv 0906.3181cond-mat.str-el
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二维量子反铁磁体Cu(tn)Cl $_2$中阻挫与磁场的相互作用

Interplay of frustration and magnetic field in the two-dimensional quantum antiferromagnet Cu(tn)Cl$_2$

A. Orendáčová, E. Čižmár, J. S. Xia, L. Yin, D. M. Pajerowski, L. Sedláková, J. Hanko, V. Zeleňák, M. Kajňaková, S. Zvyagin, M. Orendáč, A. Feher, J. Wosnitza, M. W. Meisel

摘要:

对二维反铁磁体Cu(tn)Cl $_{2}$(tn = C $_{3}$ H $_{10}$ N $_{2}$)进行了低温($T \geq 40$ mK)和强磁场($B \leq 14$ T)下的比热和交流磁化率测量.该化合物代表由具有最近邻($J/k_{B} = 3$ K)、挫败次最近邻($0 < J^{\prime}/J < 0.6$)和层间($|J^{\prime \prime}/J| \approx 10^{-3}$)相互作用的正方形晶格实现的$S = 1/2$空间各向异性三角形磁体。在$B = 0$中没有低至$T = $ 60 mK的长程磁序,以及$T \leq 0.4$ K和$B \geq 0$的比热的$T^{2}$行为被认为是高度二维磁序的证据。在低于饱和场,$B_{\text{sat}} = 6.6$ T,一个比热异常,出现在0.8 K附近,归因于绑定涡-反涡对稳定的所施加的磁场。得到的磁相图是非常一致的理想的正方形晶格的预测,除了$B_{\text{sat}}$被移动到低于预期的值。对这一现象的可能解释,以及空间各向异性三角形磁铁与Néel基态的Berezinski-Kosterlitz-BKT相变的可能性进行了讨论。

英文摘要:

Specific heat and ac magnetic susceptibility measurements, spanning low temperatures ($T \geq 40$ mK) and high magnetic fields ($B \leq 14$ T), have been performed on a two-dimensional (2D) antiferromagnet Cu(tn)Cl$_{2}$ (tn = C$_{3}$H$_{10}$N$_{2}$). The compound represents an $S = 1/2$ spatially anisotropic triangular magnet realized by a square lattice with nearest-neighbor ($J/k_{B} = 3$ K), frustrating next-nearest-neighbor ($0 < J^{\prime}/J < 0.6$), and interlayer ($|J^{\prime \prime}/J| \approx 10^{-3}$) interactions. The absence of long-range magnetic order down to $T = $ 60 mK in $B = 0$ and the $T^{2}$ behavior of the specific heat for $T \leq 0.4$ K and $B \geq 0$ are considered evidence of high degree of 2D magnetic order. In fields lower than the saturation field, $B_{\text{sat}} = 6.6$ T, a specific heat anomaly, appearing near 0.8 K, is ascribed to bound vortex-antivortex pairs stabilized by the applied magnetic field. The resulting magnetic phase diagram is remarkably consistent with the one predicted for the ideal square lattice, except that $B_{\text{sat}}$ is shifted to values lower than expected. Potential explanations for this observation, as well as the possibility of a Berezinski-Kosterlitz-Thouless (BKT) phase transition in a spatially anisotropic triangular magnet with the Néel ground state, are discussed.

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