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arXiv 1303.0619cond-mat.str-el
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海森堡正方晶格S=1/2反铁磁体Cu(pz)2(ClO4)2的各向异性和phase diagram的转变

Switching of anisotropy and phase diagram of a Heisenberg square lattice S=1/2 antiferromagnet Cu(pz)2(ClO4)2

K. Yu. Povarov, A. I. Smirnov, C. P. Landee

摘要:

准二维$S=1/2$准正方晶格反铁磁体Cu(pz)2(ClO 4)2的反铁磁相实验揭示了双轴型各向异性,而不是以前考虑的易平面型.弱的面内各向异性,发现通过电子自旋共振谱和磁化测量,是约一个数量级弱,比离面各向异性。弱的面内各向异性导致沿易磁化轴排列的磁场的自旋翻转相变,从而导致相图上的双临界点。弱面内各向异性的一个显著特征是其符号在自旋翻转点处的突变。在平面内磁场向易磁化轴倾斜10 ° $^\circ$角时,这种各向异性切换消失。突然的各向异性反转的性质仍然不清楚。相图的特点是有序化温度的增加,在磁场使用,除了双临界点附近的下降。

英文摘要:

Experiments in the antiferromagnetic phase of a quasi 2D $S=1/2$ quasi-square lattice antiferromagnet Cu(pz)2(ClO4)2 reveal a biaxial type of the anisotropy, instead of the easy-plane one, considered before. The weak in-plane anisotropy, found by means of electron spin resonance spectroscopy and magnetization measurements, is about an order of magnitude weaker, than the off-plane anisotropy. The weak in-plane anisotropy results in a spin-flop phase transition for the magnetic field aligned along easy axis, and, thereby, in a bicritical point on the phase diagram. A remarkable feature of the weak in-plane anisotropy is the abrupt change of its sign at the spin-flop point. This anisotropy switching disappears at the tilting of magnetic field to the easy axis by the angle of 10$^\circ$ within the plane. The nature of the abrupt anisotropy reversal remains unclear. The phase diagram is characterized by the increase of the ordering temperature in the magnetic field used, except for a dip near the bicritical point.

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