Neutron diffraction experiments have been carried out on a Sn-flux grown BaFe2As2 single crystal, the parent compound of the A-122 family of FeAs-based high-Tc superconductors. A tetragonal to orthorhombic structural phase transition and a three dimensional long-range antiferromagnetic ordering of the iron moment, with a unique magnetic propagation wavevector k = (1, 0, 1), have been found to take place at ~90 K. The magnetic moments of iron are aligned along the long a axis in the low temperature orthorhombic phase (Fmmm with b<a<c). Our results thus demonstrate that the magnetic structure of BaFe2As2 single crystal is the same as those in other A-122 iron pnictides compounds. We argue that the tin incorporation in the lattice is responsible for a smaller orthorhombic splitting and lower Neel temperature T_N observed in the experiment.
Reply to ``Comment on `Magnetic field effects on neutron diffraction in the antiferromagnetic phase of $UPt_3$'''
Fak，van Dijk和Wills（FDW）质疑我们对UPt_3反铁磁相弹性中子散射实验的解释。他们指出，我们的分析是不正确的，因为我们平均了对称性不允许的磁结构。我们不同意外籍家政工人的意见，并对他们的批评作出回应。FDW还指出，在N. H. van Dijk等人[Phys.Rev.B58，3186（1998）]。我们纠正了这个错误，并注意到我们以前的结论对于正确的场方向也是有效的。
We report experimental evidence of formation of antiferromagnetic clusters in composites made of a cuprate superconductor La1.85Sr0.15CuO4 (LCu) and a ferromagnet La0.6Sr0.4CoO3 (LCo). From linear and non-linear ac-susceptibility measurement on this composite material it is found that the exchange field of LCo suppress the dynamic antiferromagnetic spin fluctuation of LCu and convert it into the short range ordered superparamagnetic type antiferromagnetic (AFM) clusters at the cost of superconducting volume fraction. These shrank superconducting volume fraction shows quantum size effect (QSE) …
Bond order in two-dimensional metals with antiferromagnetic exchange interactions
我们提出了一个不受限制的Hartree-Fock计算的电荷排序不稳定性的二维金属与反铁磁交换相互作用，允许任意顺序的波矢和内部波函数的粒子-空穴对凝聚。我们发现，订购有一个占主导地位的d对称性的旋转晶格点的范围内订购波矢，包括在最近的实验中观察到的在低温下的YBCO。这种d对称性意味着电荷排序主要是在铜晶格的键上，我们提出了欠掺杂铜酸盐的无公度键序参量。金属中Neel序起始的场论有一个突现的赝自旋对称性，它将d波库珀对“旋转”为粒子-空穴对（Metlitski et al. arXiv：1005.1288）：我们的结果表明，即使自旋关联是短程和不公度的，这种对称性也会产生影响。
Crystal and Magnetic Structure of CaCo{1.86}As2 Studied by X-ray and Neutron Diffraction
中子和X射线衍射测量粉末和单晶的CaCo{1.86} As 2。晶体结构是如先前所报道的双列-四列ThCr 2Si 2型结构，但在Co位点上具有7（1）%的空位，对应于组成CaCo{1.86（2）} As 2。从10到300 K，a轴和c轴的热膨胀系数都是正的。单晶的中子衍射测量表明，在低于Neel温度TN = 52（1）K时，A型共线反铁磁有序开始出现，有序磁矩沿四角晶系c轴取向，在ab平面内铁磁排列，沿c轴反铁磁堆叠。
Suppression of magnetic order in CaCo$_{1.86}$As$_{2}$ with Fe substitution: Magnetization, neutron diffraction, and x-ray diffraction studies of Ca(Co$_{1-x}$Fe$_{x}$)$_{y}$As$_{2}$
磁化，中子衍射，高能X射线衍射结果的Sn助熔剂生长的单晶样品的Ca（Co $_{1-x}$ Fe $_{x}$）$_{y}$作为$_{2}$，$0\leq x\leq1$，$1.86\leq y \leq 2$，并显示A型反铁磁秩序，与有序的时刻位于沿$c$轴，持续为$x\lesssim0.12(1)$。随着$x$的增加，反铁磁序被平滑地抑制，有序矩和Néel温度都线性降低。$x\leq0.25$不出现条纹型反铁磁序，$x$也不出现铁磁序，至少达到$x=0.104$，并且发生从CaCo $_{1.86}$ As $_{2}$的四重（cT）相到CaFe $_{2}$ As $_{2}$的四重（T）相的平滑交叉。这些结果表明，空穴掺杂CaCo $_{1.86}$ As $_{2}$对磁性和结构的影响不如Sr取代Ca的空间效应显著。
Neutron-Diffraction Measurements of an Antiferromagnetic Semiconducting Phase in the Vicinity of the High-Temperature Superconducting State of K$_x$Fe$_{2-y}$Se$_2$
最近发现的K-Fe-Se高温超导体引起了关于其母体化合物性质的激烈争论。输运、角分辨光电子能谱和STM测量表明，它的母体化合物可能是绝缘的、半导体的甚至是金属的[M. H.方，H.- D.王角H.董志J. Li，C.- M. Feng，J. Chen，and H. Q.袁，欧罗巴。Lett. 94，27009（2011）; F. Chen等人Phys.Rev.X1，021020（2011）;和W. Li等人，物理修订信函109，057003（2012）]。由于与这些不同相关联的磁性基态尚未被识别，磁性和超导性之间的关系也没有完全理解，因此该系统的真正母体化合物仍然难以捉摸。在这里，我们报告的中子衍射实验，揭示了一个半导体反铁磁（AFM）阶段与菱形铁空位秩序。半导体相的磁性顺序与铁磷属元素化物母体化合物的条纹AFM顺序相同。此外，当root 5 * root 5块AFM相与超导性共存时，条纹AFM有序被抑制，这使我们推测新的半导体磁性有序相是该超导体的真正母相。
