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arXiv 1602.08288cond-mat.str-el
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准二维自旋1/2海森堡反铁磁体的压力和磁场效应

Pressure and magnetic field effects on a quasi-2D spin-1/2 Heisenberg antiferromagnet

N. Barbero, T. Shiroka, C. P. Landee, M. Pikulski, H. -R. Ott, J. Mesot

摘要:

Cu(pz)2(ClO 4)2(pz表示吡嗪,C4 H4 N2)是二维自旋1/2正方晶格反铁磁体的最佳实现之一。在T_N = 4.21 K以下,弱的层间耦合诱导出三维磁序,并强烈地受外部磁场和/或流体静压的影响。以前的工作,专注于[H,T]相图,确定了自旋翻转过渡,导致在现场可调双临界点。然而,外部压力的影响尚未被研究。在这里,我们探索扩展的[p,H,T]相图的Cu(pz)2(ClO 4)2下的压力高达12千巴和磁场高达7.1 T,通过磁力计和35 Cl核磁共振(NMR)测量。磁场的应用提高了T_XY,从海森堡到XY模型的交叉温度,从而指向有效各向异性的增强。外加压力的作用与此相反[dT_N/dp = 0.050(8)K/kbar],它对层间耦合的影响很小,但对轨道重取向和正方晶格形变的影响可能更大。这导致有效哈密顿量的重构,由此场效应和压力效应相互补偿。最后,通过比较实验数据与数值模拟,我们估计T_BKT,Berezinskiii-Kosterlitz-无边界拓扑转变的温度,并讨论为什么它是不可访问的,在我们的情况下。

英文摘要:

Cu(pz)2(ClO4)2 (with pz denoting pyrazine, C4H4N2) is among the best realizations of a two-dimensional spin-1/2 square-lattice antiferromagnet. Below T_N = 4.21 K, its weak interlayer couplings induce a 3D magnetic order, strongly influenced by external magnetic fields and/or hydrostatic pressure. Previous work, focusing on the [H, T] phase diagram, identified a spin-flop transition, resulting in a field-tunable bicritical point. However, the influence of external pressure has not been investigated yet. Here we explore the extended [p, H, T] phase diagram of Cu(pz)2(ClO4)2 under pressures up to 12 kbar and magnetic fields up to 7.1 T, via magnetometry and 35Cl nuclear magnetic resonance (NMR) measurements. The application of magnetic fields enhances T_XY , the crossover temperature from the Heisenberg to the XY model, thus pointing to an enhancement of the effective anisotropy. The applied pressure has an opposite effect [dT_N/dp = 0.050(8) K/kbar], as it modifies marginally the interlayer couplings, but likely changes more significantly the orbital reorientation and the square-lattice deformation. This results in a remodeling of the effective Hamiltonian, whereby the field and pressure effects compensate each other. Finally, by comparing the experimental data with numerical simulations we estimate T_BKT, the temperature of the Berezinskii-Kosterlitz-Thouless topological transition and argue why it is inaccessible in our case.

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