利用小角中子散射和SQUID测量研究了赝二元化合物Mn $_{1-x}$ Co $_{x}$ Ge的磁性系统。发现在$x \in [0 ÷0.9]$的整个浓度范围内，Mn $_{1-x}$ Co $_{x}$ Ge在低温下是磁性有序的.已经发现了三种不同的磁结构状态：在$x \leq 0.45$处的短周期螺旋状态、在$0.45 < x \leq 0.8$处的长周期螺旋状态和在$x \sim 0.9$处的铁磁状态。考虑到相对大的螺旋波矢$k \gg 1$ nm $^{-1}$是主要与Ruderman-Kittel-Kasuya-Yoshida（RKKY）相互作用的系统的特征，我们建议，在$x \leq 0.45$的短周期螺旋结构是基于一个有效的RKKY相互作用。此外，随着$x$的增加，$k$的衰减归因于第二近邻之间的相互作用的减少，因此，Dzyaloshinskiy-Moriya相互作用的影响增加。作为这两种相互作用之间的竞争的结果，从长程有序（LRO）到短程有序（SRO）的螺旋结构的量子相变已被观察到后，在$x_{c1} \sim 0.25$的Co浓度的增加。$x$的进一步增加导致在$0.45 < x < 0.7$处的散射分布中出现双峰。在$x = 0.9$发现的从螺旋结构到铁磁状态的转变是由于与立方各向异性相比，铁磁的减弱引起的。总之，Mn $_{1-x}$ Co $_{x}$ Ge的磁结构随着$x$的增加而演变是从基于有效RKKY相互作用的螺旋结构到铁磁结构的连续转变的示例，该连续转变穿过基于RKKY相互作用的螺旋结构。
英文摘要：
The magnetic system of the pseudobinary compound Mn$_{1-x}$Co$_{x}$Ge has been studied using small-angle neutron scattering and SQUID-measurements. It is found that Mn$_{1-x}$Co$_{x}$Ge orders magnetically at low temperatures in the whole concentration range of $x \in [0 ÷0.9]$. Three different states of the magnetic structure have been found: a short-periodic helical state at $x \leq 0.45$, a long-periodic helical state at $0.45 < x \leq 0.8$, and a ferromagnetic state at $x \sim 0.9$. Taking into account that the relatively large helical wavevector $k \gg 1$ nm$^{-1}$ is characteristic for systems with mainly Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction, we suggest that the short-periodic helical structure at $x \leq 0.45$ is based on an effective RKKY interaction. Also the decay of $k$ with increasing $x$ is ascribed to a reduction of the interaction between second nearest neighbors and, therefore, to an increase of the influence of the Dzyaloshinskiy-Moriya interaction (DMI). As a result of the competition between these two interactions the quantum phase transition from a long-range ordered (LRO) to a short-range ordered (SRO) helical structure has been observed upon increase of the Co-concentration at $x_{c1} \sim 0.25$. Further increase of $x$ leads to the appearance of a double peak in the scattering profile at $0.45 < x < 0.7$. The transition from a helical structure to a ferromagnetic state found at $x = 0.9$ is caused by the weakening of DMI as compared to the cubic anisotropy. In summary, the evolution of the magnetic structure of Mn$_{1-x}$Co$_{x}$Ge with increasing $x$ is an example of a continuous transition from a helical structure based on the effective RKKY interaction to a ferromagnetic structure passing through a helical structure based on DMI.
We report on a sequence of field-induced transitions in the zigzag ladder compound BaDy2O4 studied with powder neutron diffraction and magnetisation measurements. In agreement with the previously published results, the low temperature zero-field structure is characterised by two half-integer propagation vectors, k1=[1/2 0 1/2] and k2= 1/2 1/2 1/2]. However, on application of an external magnetic field, the Bragg peaks corresponding to the zero-field structure lose their intensity rather rapidly and disappear completely in a field of 2.5 kOe. In the intermediate fields, 2.5 to 22.5 kOe, new pea…
Temperature and composition phase diagram in the iron-based ladder compounds Ba1-xCsxFe2Se3
研究了铁基梯形化合物（Ba，Cs）Fe $_2$ Se $_3$ .它们的母体化合物BaFe $_2$ Se $_3$和CsFe $_2$ Se $_3$具有不同的空间群、Fe的价态和磁性结构。通过电阻率、比热容、磁化率、X射线衍射和粉末中子衍射等测量，得到了该体系的温度和组成相图。在BaFe $_2$ Se $_3$中观察到的块磁性被Cs掺杂显著抑制。相比之下，在CsFe $_2$ Se $_3$中观察到的条带磁性对于Ba掺杂不是如此脆弱。在中间组分中出现了新的磁性结构，类似于CsFe $_2$ Se $_3$的条形磁性，但梯间自旋组态不同。中间化合物显示绝缘行为，然而有限的$T$ -线性贡献的比热在低温下获得。
Superconductivity in FeSe is strongly enhanced under applied pressure and it is proposed to emerge from anomalously coupled structural and magnetic phases. Small impurities inside the Fe plane can strongly disrupt the pair formation in FeSe at ambient pressure and can also reveal the interplay between normal and superconducting phases. Here, we investigate how an impurity inside the Fe plane induced by the Cu substitution can alter the balance between competing electronic phases of FeSe at high pressures. In the absence of an applied magnetic field, at low pressures the nematic and superconduc…
Limitations of unconstrained LSDA+$U$ calculations in predicting the electronic and magnetic ground state of a geometrically frustrated ZnV$_{2}$O$_{4}$ compound
The current efforts to find the materials hosting Kitaev model physics have been focused on Mott insulators of d^5 pseudospin-1/2 ions Ir^{4+} and Ru^{3+} with t_{2g}^5(S=1/2, L=1) electronic configuration. Here we propose that the Kitaev model can be realized in materials based on d^7 ions with t_{2g}^5e_g^2(S=3/2, L=1) configuration such as Co^{2+}, which also host the pseudospin-1/2 magnetism. Considering possible exchange processes, we have derived the d^7 pseudospin-1/2 interactions in 90^{\circ} bonding geometry. The obtained Hamiltonian comprises the bond-directional Kitaev K and isotro…
Using the density-matrix renormalization group technique, we study a one-dimensional spin-$\frac{1}{2}$ Heisenberg chain consisting of coupled tetramers as an effective spin model for copper vanadate CuInVO$_5$. We obtain the ground-state phase diagram as a function of intra-tetramer and inter-tetramer exchange interactions, exhibiting two multimerized valence-bond-solid (VBS) phases : one is characterized by the formation of tetramer-singlet units; the other by the formation of dimer-singlet pairs. We show that the finite spin gaps in both the VBS phases smoothly vanish at the phase boundary:…
Double perovskite iridates $A_2$ZnIrO$_6$ ($A$ = alkaline or lanthanide) show complex magnetic behaviors ranging from weak ferromagnetism to successive antiferromagnetic transitions. Here we report the static ($dc$) and dynamic ($ac$) magnetic susceptibility, and neutron powder diffraction measurements for $A$ = La and Nd compounds to elucidate the magnetic ground state. Below 10~K, the $A$ = La compound is best described as canted iridium moments in an antiferromagnet arrangement with a propagation vector \textbf{k} = 0 and a net ferromagnetic component along the $c$-axis. On the other hand, …
Structural and magnetic properties of two branches of the Tripod Kagome Lattice family A$_{2}$RE$_{3}$Sb$_{3}$O$_{14}$ (A = Mg, Zn; RE = Pr, Nd, Gd, Tb, Dy, Ho, Er, Yb)
本文系统地研究了稀土三脚架Kagome晶格（TKL）族的两个分支的结构和磁性（A = Mg，Zn; RE = Pr，Nd，Gd，Tb，Dy，Ho，Er，Yb;这里，我们使用缩写\textit{A-RE}，如在\textit{MgPr}中表示Mg $_{2}$ Pr $_{3}$ Sb $_{3}$ O $_{14}$），其补充了我们先前报道的关于\textit{MgDy}、\textit{MgGd}和\textit{MgEr} \cite{TKL}的工作。目前的易感性（$χ_{dc}$，$χ_{ac}$）和比热测量揭示了各种磁性基态，包括\textit{MgPr}，\textit{ZnPr}的非磁性单线态; \textit{MgGd}，\textit{ZnGd}，\textit{MgNd}，\textit{ZnNd}和\textit{MgYb}的长程有序（LRO）; \textit{MgDy}，\textit{ZnDy}和潜在的\textit{MgHo}的长程磁荷有序态; \textit{ZnEr}、\textit{ZnHo}可能的自旋玻璃态; \textit{MgEr}、\textit{MgTb}、\textit{ZnTb}和\textit{ZnYb}化合物在80 mK以下不存在自旋有序。在这里观察到的基态既有相似之处，也有显着的差异，从父母烧绿石系统中发现的国家。特别是，虽然T…
Evolution of band structure from optimally doped to heavily overdoped Co-substituted NaFeAs
用角分辨光电子能谱研究了NaFe $_{1-x}$ Co $_x$ As从最佳掺杂超导化合物（$x=0.028$）到重过掺杂非超导化合物（$x=0.109$）的电子结构。与“122”型铁磷属元素化合物的情况类似，我们的数据表明，在NaFe $_{1-x}$ Co $_x$ As中的Co掺杂提供了额外的载流子，并相应地移动了费米能级。在$x=0.109$化合物中，围绕带中心$Γ$的空穴状带移动到更深的结合能，而出现电子口袋。在整个掺杂范围内，我们研究的整体能带重整化基本上保持不变，这表明局部磁/电子相关性不受载流子掺杂的影响。我们推测，流动载流子的巡游特性和局域相互作用之间的平衡可能对超导性起着重要的作用。
The robustness of spin liquids with respect to small perturbations, and the way magnetic frustration can be lifted by slight changes in the balance between competing magnetic interactions remains a rich and open issue. We address this question through the study of the Gadolinium Aluminium garnet Gd$_3$Al$_5$O$_{12}$, a related compound to the extensively studied Gd$_3$Ga$_5$O$_{12}$. We report on its magnetic properties at very low temperature. We show that despite a freezing at about 300 mK, no magnetic transition is observed, suggesting the presence of a spin liquid state down to the lowest …
Recently, the bi-layer Kagome lattice material Ca$_{10}$Cr$_7$O$_{28}$ has been shown to be a quasi-two-dimensional quantum spin liquid (QSL) where the frustration arises from a balance between competing ferromagnetic and antiferromagnetic exchange within a bi-layer. In an attempt to understand what happens when this balance is disturbed, we present a magnetic dilution study. Specifically, we have synthesized Ca$_{10}$(Cr$_{1-x}$V$_x$)$_7$O$_{28}$ (0 $\leq$ x $\leq$ 0.5) where magnetic Cr$^{5+}$ ($S = 1/2$) is partially replaced by non-magnetic V$^{5+}$ ($S = 0$). We also synthesized the fully…
