Transport properties of the classical antiferromagnetic XXZ model on the square lattice have been theoretically investigated, putting emphasis on how the occurrence of a phase transition is reflected in spin and thermal transports. As is well known, the anisotropy of the exchange interaction $Δ\equiv J_z/J_x$ plays a role to control the universality class of the transition of the model, i.e., either a second-order transition at $T_N$ into a magnetically ordered state or the Kosterlitz-Thouless (KT) transition at $T_{KT}$, which respectively occur for the Ising-type ($Δ>1$) and $XY$-type ($Δ<1$) anisotropies, while for the isotropic Heisenberg case of $Δ=1$, a phase transition does not occur at any finite temperature. It is found by means of the hybrid Monte-Carlo and spin-dynamics simulations that the spin current probes the difference in the ordering properties, while the thermal current does not. For the $XY$-type anisotropy, the longitudinal spin-current conductivity $σ^s_{xx}$ ($=σ^s_{yy}$) exhibits a divergence at $T_{KT}$ of the exponential form, $σ^s_{xx} \propto \exp\big[ B/\sqrt{T/T_{KT}-1 }\, \big]$ with $B={\cal O}(1)$, while for the Ising-type anisotropy, the temperature dependence of $σ^s_{xx}$ is almost monotonic without showing a clear anomaly at $T_{N}$ and such a monotonic behavior is also the case in the Heisenberg-type spin system. The significant enhancement of $σ^s_{xx}$ at $T_{KT}$ is found to be due to the exponential rapid growth of the spin-current-relaxation time toward $T_{KT}$, which can be understood as a manifestation of the topological nature of a vortex whose lifetime is expected to get longer toward $T_{KT}$. Possible experimental platforms for the spin-transport phenomena associated with the KT topological transition are discussed.
Interplay of anisotropy and frustration: triple transitions in a triangular-lattice antiferromagnet
本文研究了三角晶格上单离子易轴各向异性的经典海森堡反铁磁体。构造了外磁场中的平均场相图。通过零场蒙特卡罗模拟，发现了三个有限温度Berezinskiii-Kosterlitz-无相变。两个上部的过渡与离散的${\mathbb Z}_{6}$对称群的破缺有关，而最低的过渡与横向分量的准长程有序有关。第一和第二转变之间的中间共线相位是由J. V. José { \it et al}预测的滑动相位。[Phys. Rev. B { \bf 16}，1217（1977）]。
Importance of In-Plane Anisotropy in the Quasi Two-Dimensional Antiferromagnet BaNi$_{2}$V$_{2}$O$_{8}$
用比热、热膨胀、磁致伸缩和垂直于$\mathbf{c}$的磁化强度研究了准二维反铁磁体BaNi $_{2}$ V $_{2}$ O $_{8}$的相图.在$μ_0H^{*}\simeq1.5$ T处，到高场状态的交叉（其中$T_N(H)$线性增加）起因于本征和场诱导的面内各向异性的竞争。$T_N$和$H^{*}$的压力依赖性解释使用的图片的压力诱导的面内各向异性。即使在零场和环境压力下，面内各向异性也不能忽略，这意味着偏离纯Berezinskiii-Kosterlitz-无轴行为。
Influence of uniaxial single-ion anisotropy on the magnetic and thermal properties of Heisenberg antiferromagnets within unified molecular field theory
Effects of an external magnetic field on the gaps and quantum corrections in an ordered Heisenberg antiferromagnet with Dzyaloshinskii-Moriya anisotropy
研究了外加磁场对具有Dzyaloshinskiii-Moriya（DM）相互作用的有序海森堡反铁磁体性质的影响.利用自旋波理论对能量、在位磁化强度和均匀磁化强度进行了量子修正，计算了它们随磁场H和DM各向异性常数D的变化关系。结果表明，自旋波激发表现出一个不寻常的领域的发展的差距。这导致了量子修正对H和D的各种非解析依赖性。它也表明，相当普遍的，DM相互作用抑制量子涨落，从而驱动系统到一个更经典的基态。大部分的讨论是专门的自旋S，二维正方形晶格反铁磁体，其S=1/2的情况下，密切实现在K2 V3 O 8，其中在H=0的DM各向异性是隐藏的易轴各向异性，但在一个有限的字段中显示。在这种材料中的自旋-激发间隙的场依赖性的理论结果和其他系统的影响进行了讨论。
Temperature induced phase transition from cycloidal to collinear antiferromagnetism in multiferroic Bi$_{0.9}$Sm$_{0.1}$FeO$_3$ driven by $f$-$d$ induced magnetic anisotropy
Tunable bifurcation of magnetic anisotropy and bi-oriented antiferromagnetic order in kagome metal GdTi3Bi4
Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学）；Department of Physics and State Key Laboratory of Surface Physics, Fudan University（复旦大学）
Relationship between Magnetic Anisotropy Below Pseudogap Temperature and Short-Range Antiferromagnetic Order in High-Temperature Cuprate Superconductor
高温铜氧化物超导体的中心问题是在赝能隙温度$T^*$以下出现的赝能隙态，赝能隙温度远高于超导转变温度。在这项研究中，我们从理论上研究了磁各向异性的快速增加低于赝能隙温度检测到的最新扭矩磁强计测量YBa $_2$ Cu $_3$ O $_y$ [Y. Sato等人，自然物理学，13，1074（2017）]。应用自旋格林函数的形式主义，包括Dzyaloshinskii-Moriya相互作用所产生的CuO $_2$平面的屈曲，我们得到的结果是在很好的协议与实验，并找到一个标度关系。我们的分析表明，与磁各向异性，这符合$T^*$的特征温度，是不是一个相变温度，但与短程反铁磁序的交叉温度。
Modified anisotropy and distinct phase diagrams in the nearly isotropic $S=1$ triangular-lattice antiferromagnet $\mathrm{Rb_2Ni(SeO_3)_2}$
Renmin University of China（中国人民大学）；Hefei Institutes of Physical Science, Chinese Academy of Sciences（中国科学院合肥物质科学研究院）；University of Tokyo（东京大学）；Southern University of Science and Technology（南方科技大学）；Great Bay University（大湾区大学）
Spin Dynamics of Layered Triangular Antiferromagnets with Uniaxial Anisotropy
本文用MonteCarlo-分子动力学方法研究了具有反铁磁耦合的三角形层状晶格上具有单轴各向异性的半经典海森堡模型在有序相和顺磁相的自旋动力学.计算的重要量是全动力学结构函数$S(\bf q, ω)$、手征动力学结构函数$S_{chi}(ω)$、静态序参量和一些热力学量。结果表明，在有序相中存在对应于$S(\bf q, ω)$和$S_{chi}(ω)$的传播模，支持了最近的理论.我们的静态性质的结果表明，在每一层的磁有序是共面的3-亚晶格类型偏离120度结构。然而，在磁三聚化的存在下，我们发现3-亚晶格结构被削弱，并趋向于自旋的非共面性。
Splitting of antiferromagnetic resonance modes in the quasi-two-dimensional collinear antiferromagnet Cu(en)(H$_2$O)$_2$SO$_4$
对准二维反铁磁体Cu（en）（H $_2$ O）$_2$ SO $_4$（en = C $_2$ H $_8$ N $_2$）进行了低温磁共振研究.该化合物在0.9K下具有反铁磁性。的共振数据的流体动力学方法内的分析允许确定各向异性轴，并估计反铁磁相的各向异性参数。偶极自旋-自旋耦合是反铁磁相各向异性的主要贡献。的共振模式的分裂和它的非单调依赖于所施加的频率被观察到低于0.6K在所有三个字段的方向。讨论了几种模型来解释Cu（en）（H $_2$ O）$_2$中非平凡分裂的起源和不等价磁子系统的存在，因此选择$_4$作为最可能的来源。
Anisotropy of the in-plane resistivity of underdoped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ superconductors induced by impurity scattering in the antiferromagnetic orthorhombic phase
研究了低掺杂Ba（Fe $_{1-x}$ Co $_x$）$_2$ As $_2$单晶的面内电阻率各向异性。我们表明，在磁结构有序相的电阻率的各向异性产生的各向异性的剩余成分中的Co浓度$x$成比例增加。这证明了各向异性起源于Co原子取代Fe位的杂质散射，而不是迄今为止提出的机制，如重建的费米表面口袋的费米速度的各向异性。随着掺杂进行到顺磁-四极相，Co杂质转变为弱的和各向同性的散射中心。
