本文报道了EuCo $_2$ As $_2$单晶的$^{153}$ Eu、$^{75}$ As和$^{59}$ Co的核磁共振谱。在反铁磁（AFM）有序温度$T_{\rm N}$ = 45 K以下的4.3 K零磁场下观测$^{153}$ Eu和$^{75}$ As的NMR谱及其对外磁场的依赖性清楚地证明了EuCo $_2$ As $_2$中的无公度螺旋AFM结构。此外，基于在顺磁和无公度AFM状态下的$^{59}$ Co NMR数据，我们确定了AFM传播矢量${\bf k}$ =（0，0，0.73 $\pm$ 0.07）2 $π$ / $c$的模型无关值，其中$c$是$c$晶格参数。因此，无公度螺旋AFM状态的特征在于只有NMR数据与模型无关的分析，显示NMR是一个独特的工具，用于确定在无公度螺旋AFM的自旋结构。
英文摘要：
We report $^{153}$Eu, $^{75}$As and $^{59}$Co nuclear magnetic resonance (NMR) results on EuCo$_2$As$_2$ single crystal. Observations of $^{153}$Eu and $^{75}$As NMR spectra in zero magnetic field at 4.3 K below an antiferromagnetic (AFM) ordering temperature $T_{\rm N}$ = 45 K and its external magnetic field dependence clearly evidence an incommensurate helical AFM structure in EuCo$_2$As$_2$. Furthermore, based on $^{59}$Co NMR data in both the paramagnetic and the incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector ${\bf k}$ = (0, 0, 0.73 $\pm$ 0.07)2$π$/$c$ where $c$ is the $c$ lattice parameter. Thus the incommensurate helical AFM state was characterized by only NMR data with model-independent analyses, showing NMR to be a unique tool for determination of the spin structure in incommensurate helical AFMs.
9Be-NMR measurements were performed using single crystalline SmBe13 in order to investigate a magnetic structure of a low-temperature ordering state microscopically. We observed a spectral broadening in the ordered state, and the broadened spectral shape depends on the magnetic field directions. By comparing the experimentally obtained and simulated NMR spectra for magnetic fields along the cubic [001] and [011] directions, we argue a helical structure with a basal plane tilted from the (001) plane in low-field ordering region under the assumption of a helical with a propagation vector of (0, …
We carried out $^{75}$As nuclear magnetic resonance (NMR) measurements on the trigonal CaMn$_2$As$_2$ and SrMn$_2$As$_2$ insulators exhibiting antiferromagnetic (AFM) ordered states below Néel temperatures $T_{\rm N}$ = 62 K and 120 K, respectively. In the paramagnetic state above $T_{\rm N}$, typical quadrupolar-split $^{75}$As-NMR spectra were observed for both systems. The $^{75}$As quadrupolar frequency $ν_{\rm Q}$ for CaMn$_2$As$_2$ decreases with decreasing temperature, while $ν_{\rm Q}$ for SrMn$_2$As$_2$ increases, showing an opposite temperature dependence.In the AFM state, the relati…
Helical scattering signatures of strain and electronic textures in YbFe2O4 from three-dimensional reciprocal space imaging
绝缘的三元氧化物YbFe $_2$ O $_4$显示出一个不寻常的阻挫驱动的无公度电荷有序（CO）转变，与可能的铁电性。基于高分辨率的同步辐射数据，我们报告了一个详细的结构模型表明，CO相是一个无公度的电荷密度波，不能铁电，因为电偶极矩也inconveniately调制。连续和“斑点”的螺旋散射在CO过渡之间的变化是由于三维波动的方向的有序波矢。
Field-induced transitions from incommensurate to commensurate phases in helical antiferromagnets
National Research University Higher School of Economics（国立高等经济大学）；Petersburg Nuclear Physics Institute named by B.P. Konstantinov of National Research Center “Kurchatov Institute”（国立库尔恰托夫研究所彼得堡核物理研究所）
Partial Antiferromagnetic Helical Order in Fe$_3$PO$_4$O$_3$
Fe $_3$ PO $_4$ O $_3$中的磁阻挫已被证明在T $_N = 163$ K以下产生不寻常的磁状态，其中无公度反铁磁序被限制于纳米尺寸的针状域，如从中子粉末衍射推断的。在这里，我们使用单晶中子衍射表明，Fe $_3$ PO $_4$ O $_3$不表现出一个优选的有序波矢量方向在$ab$平面，尽管有一个明确的有序波矢量长度。这导致观察到连续的散射环，而不是卫星布拉格峰。缺乏一个优选的无公度有序波矢量方向可以理解为一个反铁磁海森堡模型与最近邻（$J_1$）和第二邻居（$J_2$）的相互作用，它产生了一个准简并流形的有序波矢量。这种状态看起来类似于MnSi的部分有序相，但在Fe $_3$ PO $_4$ O $_3$中产生受抑反铁磁体而不是手性铁磁体。
Long-range ordering of magnetic dipoles in bulk materials gives rise to a broad range of magnetic structures, from simple collinear ferromagnets and antiferromagnets, to complex magnetic helicoidal textures stabilized by competing exchange interactions. In contrast, in the context of dipolar order in dielectric crystals, only parallel (ferroelectric) and antiparallel (antiferroelectric) collinear alignments of electric dipoles are typically considered. Here, we report an observation of incommensurate helical ordering of electric dipoles by light hole-doping of the quadruple perovskite BiMn7O12…
We use neutron scattering to investigate spin excitations in Sr(Co$_{1-x}$Ni$_{x})_2$As$_2$, which has a $c$-axis incommensurate helical structure of the two-dimensional (2D) in-plane ferromagnetic (FM) ordered layers for $0.013\leq x \leq 0.25$. By comparing the wave vector and energy dependent spin excitations in helical ordered Sr(Co$_{0.9}$Ni$_{0.1}$)$_2$As$_2$ and paramagnetic SrCo$_2$As$_2$, we find that Ni-doping, while increasing lattice disorder in Sr(Co$_{1-x}$Ni$_{x})_2$As$_2$, enhances quasi-2D FM spin fluctuations. However, our band structure calculations within the combined densi…
We report a detailed study of the ground state helical magnetic structure in monophosphide FeP by means of ${}^{31}$P NMR spectroscopy. We show that the zero-field NMR spectrum of the polycrystalline sample provides strong evidence of an anisotropic distribution of local magnetic fields at the P site with substantially lower anharmonicity than that found at the Fe site by Mössbauer spectroscopy. From field-sweep ${}^{31}$P NMR spectra we conclude that a continuous spin-reorientation transition occurs in an external magnetic field range of 4 - 7 T, which is also confirmed by specific-heat measu…
Neutron diffraction on the centrosymmetric square-net magnet EuGa$_2$Al$_2$ reveals multiple incommensurate magnetic states (AFM1,2,3) in zero field. In applied field, a new magnetic phase (A) is identified from magnetization and transport measurements, bounded by two of the $μ_0H$~=~0 incommensurate magnetic phases (AFM1,helical and AFM3, cycloidal) with different moment orientations. Moreover, magneto-transport measurements indicate the presence of a topological Hall effect, with maximum values centered in the A phase. Together, these results render EuGa$_2$Al$_2$ a material with non-coplana…
Magnetization, magnetic torque, neutron diffraction and NMR experiments are used to map out the $H$$-$$T$ phase diagram of the prototypical quasi-two-dimensional ferro-antiferromagnet Pb$_2$VO(PO$_4$)$_2$ in magnetic fields up to 27 T. When the field is applied perpendicular to the axis of magnetic anisotropy, a new magnetic state emerges through a discontinuous transition and persists in a narrow field range just below saturation. The measured NMR spectra suggest a complex and possibly incommensurate magnetic order in that regime.
In frustrated magnetic systems, the competition amongst interactions can introduce extremely high degeneracy and prevent the system from readily selecting a unique ground state. In such cases, the magnetic order is often exquisitely sensitive to the balance among the interactions, allowing tuning among novel magnetically ordered phases. In antlerite, Cu$_3$SO$_4$(OH)$_4$, Cu$^{2+}$ ($S=1/2$) quantum spins populate three-leg zigzag ladders in a highly frustrated quasi-one-dimensional structural motif. We demonstrate that at zero applied field, in addition to its recently reported low-temperatur…
