We describe neutron scattering experiments performed to investigate the magnetic order and dynamics of half-doped La1.5Sr0.5CoO4. This layered perovskite exhibits a near-ideal checkerboard pattern of Co2+/Co3+ charge order at temperatures below ~ 800 K. Magnetic correlations are observed at temperatures below ~ 60 K but static magnetic order only becomes established at 31 K, a temperature at which a kink is observed in the susceptibility. On warming above 31 K we observed a change in the magnetic correlations which we attribute either to a spin canting or to a change in the proportion of inequivalent magnetic domains. The magnetic excitation spectrum is dominated by an intense band extending above a gap of approximately 3 meV up to a maximum energy of 16 meV. A weaker band exists in the energy range 20-30 meV. We show that the excitation spectrum is in excellent quantitative agreement with the predictions of a spin-wave theory generalized to include the full magnetic degrees of freedom of high-spin Co2+ ions in an axially distorted crystal field, coupled by Heisenberg exchange interactions. The magnetic order is found to be stabilized by dominant antiferromagnetic Co2+ -- Co2+ interactions acting in a straight line through Co3+. No evidence is found for magnetic scattering from the Co3+ ions, supporting the view that Co3+ is in the S = 0 state in this material.
We measured magnetization, specific heat, electron spin resonance, neutron diffraction, and inelastic neutron scattering of CrVMoO$_7$ powder. An antiferromagnetically ordered state appears below $T_{\rm N} = 26.5 \pm 0.8$ K. We consider that the probable spin model for CrVMoO$_7$ is an interacting antiferromagnetic spin-$\frac{3}{2}$ dimer model. We evaluated the intradimer interaction $J$ to be $25 \pm 1$ K and the effective interdimer interaction $J_{\rm eff}$ to be $8.8 \pm 1$ K. CrVMoO$_7$ is a rare spin dimer compound that shows an antiferromagnetically ordered state at atmospheric press…
A quantitative description of magnons in long-range ordered quantum antiferromagnets is presented which is consistent from low to high energies. It is illustrated for the generic $S=1/2$ Heisenberg model on the square lattice. The approach is based on a continuous similarity transformation in momentum space using the scaling dimension as truncation criterion. Evidence is found for significant magnon-magnon attraction inducing a Higgs resonance. The high-energy roton minimum in the magnon dispersion appears to be induced by strong magnon-Higgs scattering.
Influence of the $A$ cation on the low-temperature antiferromagnetism of ordered antiferroelectric $A_2$CoTeO$_6$ perovskites
我们研究了反铁电$A_2$ CoTeO $_6$钙钛矿（其中$A$ = Cd，Ca，Sr，Pb，Ba）的结构和磁性。所有化合物在低温下都是反铁磁性的，反铁磁性转变温度随着$A$阳离子的离子尺寸的减小而略微降低。在$A^{2+}_2$ Co $M^{6+}$ O $_6$材料中没有观察到反铁磁相互作用的这种减少，这表明Te $^{6+}$阳离子影响系统的电子结构，进而影响系统的磁结构。
We propose in this work an effective field theory description of the chiral spin liquid state in Heisenberg spin system on kagomé lattice.To this end, we derive the low-energy effective theory of kagomé (isotropic) Heisenberg antiferromagnet around its ordered ground states found numerically and show that quantum fluctuations induced by further neighbor spin exchanges are equally strong as those from first neighbor.We use a chiral order parameter theory to argue for the occurrence of finite temperature chiral symmetry breaking transition into chiral ordered state in kagomé antiferromagnet with…
We present the magnetic phase diagram of a spin-1/2 chain antiferromagnet Sr$_2$CuO$_3$ studied by ultrasound phase-sensitive detection technique. We observe an enhanced effect of external magnetic field on the ordering temperature of the system, which is in the extreme proximity to the quantum critical point. Inside the Néel ordered phase, we detect an additional field-induced continuous phase transition, which is unexpected for a collinear Heisenberg antiferromagnet. This transition is accompanied by softening of magnetic excitation mode observed by electron-spin resonance, which can be asso…
Magnetic order in Tb$_2$Sn$_2$O$_7$ under high pressure: from ordered spin ice to spin liquid and antiferromagnetic order
本文用中子衍射方法研究了Tb $_2$ Sn $_2$ O $_7$阻挫磁体在4.6 GPa各向同性压力和0.3 GPa单轴压力下，温度范围为0.06 K $<$ T $<$ 100 K。磁性秩序下的压力，但有序的自旋冰结构稳定在低于1.3 K的环境压力部分转化为反铁磁的。在0.06 K下的长程有序矩在压力下减少，这是由压力引起的自旋液体波动的增强解释。在有序转变之上，短程自旋关联受到压力的影响，铁磁关联被抑制。考虑各向同性效应和应力效应，讨论了压力对基态的影响。
Crossover from impurity-induced ordered phase to uniform antiferromagnetic phase under hydrostatic pressure in the doped spin-gap system TlCu$_{1-x}$Mg$_x$Cl$_3$
We present an experimental study of macroscopic and microscopic magnetic anisotropy of a spin tetramer system \cso using torque magnetometry and ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature observed from torque magnetometry agrees reasonably well with the rotation of the $\mathbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\mathbf{g}$ tensor is temperature independent, while macroscopic magnetic axes continue to rotate. Additionally, the susceptibility anisotropy has a temperature dependence which cannot be reconciled with the isotropic Heisenberg mode…
Field-induced gap in ordered Heisenberg antiferromagnets
在强均匀磁场$H$中，海森堡反铁磁体将呈现出全局O（2）对称的无隙相.在许多实际磁体中，小的能隙由附加的相互作用引起，该附加的相互作用可以被视为交错的横向磁场$h = c H$，其中$c$是小的比例常数。我们研究这样的扰动的影响，特别是与长程序的磁铁，通过使用几个互补的方法：数值对角化的模型与长程相互作用，经典的运动方程，和缩放参数。在零温度下的有序状态中，能隙首先以$(cH)^{1/2}$的形式增长，然后可能在将“无隙”相与具有饱和磁化的带隙状态分离的量子临界点处下降到$(cH)^{2/3}$阶的较小值。在一个空间维度中，后一个指数变为4/5。
The thermodynamics of the antiferromagnetic ordering transition in NiO and the photoelectron spectra in the antiferromagnetic phase are studied by the Variational Cluster Approximation. Using realistic Racah parameters to describe the Coulomb interaction in the Ni 3d shell and a Slater-Koster parameter pds which is slightly (10%) increased over the band structure estimate the calculated Neel temperature is 481 Kelvin (experimental value: 523 Kelvin). The magnetic susceptibility above TN has Curie-Weiss form. A significant contribution to the stabilization of the antiferromagnetic phase comes f…
We carried out inelastic neutron scattering experiments on a buckled honeycomb lattice antiferromagnet Ba$_{2}$NiTeO$_{6}$ exhibiting a stripe structure at a low temperature. Magnetic excitations are observed in the energy range of $\hbar ω\lesssim 10$ meV having an anisotropy gap of 2 meV at 2 K. We perform spin-wave calculations to identify the spin model. The obtained microscopic parameters are consistent with the location of the stripe structure in the classical phase diagram. Furthermore, the Weiss temperature independently estimated from a bulk magnetic susceptibility is consistent with …
A-site ordered perovskites, CaCu$_3$B$_4$O$_{12}$, which are derivatives of conventional ABO$_3$ perovskites, exhibit varying electronic and magnetic properties. With the objective of examining the role of Cu in this work, we have studied CaCu$_3$Ti$_4$O$_{12}$ and CaCu$_3$Zr$_4$O$_{12}$ and presented the cause of the crystallization of A-site ordered perovskite from conventional ABO$_3$ perovskite and the underlying mechanism leading to the stabilization of non-trivial and experimentally estabilished G-type antiferromagnetic (G-AFM) ordering in these systems. The first-principles electronic s…
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。
We study a generalized quantum spin ladder with staggered long range interactions that decay as a power-law with exponent $α$. Using large scale quantum Monte Carlo (QMC) and the density matrix renormalization group (DMRG) simulations, we show that this model undergoes a transition from a rung-dimer phase characterized by a non-local string order parameter, to a symmetry broken Néel phase. We find evidence that the transition is second order.In the magnetically ordered phase, the spectrum exhibits gapless modes, while excitations in the gapped phase are well described in terms of triplons -- b…
We study a generalized quantum spin ladder with staggered long range interactions that decay as a power-law with exponent $α$. Using large scale quantum Monte Carlo (QMC) and density matrix renormalization group (DMRG) simulations, we show that this model undergoes a transition from a rung-dimer phase characterized by a non-local string order parameter, to a symmetry broken Néel phase. We find evidence that the transition is second order. In the magnetically ordered phase, the spectrum exhibits gapless modes, while excitations in the gapped phase are well described in terms of triplons -- boun…
The Goldstone theorem mandates that a spontaneous symmetry breaking entails the emergence of gap(mass)less excitations. In the case where a rotational invariance of a system of spin magnetic moments is broken by an antiferromagnetic order, these are well-known transverse spin waves. The interaction of such Goldstone magnons with the Higgs amplitude mode of the order parameter is usually discarded, even though glimpses of Higgs physics have recently been reported in a quantum magnet, a topological insulator, and ferroelectric and disordered superconductor systems. The Goldstone-Higgs interactio…
We have systematically investigated the variation of the exchange parameters and the ground state in the $S = 1/2$ kagome-lattice antiferromagnet (Rb$_{1-x}$Cs$_{x}$)$_2$Cu$_3$SnF$_{12}$, via magnetic measurements using single crystals. One of the parent compounds, Rb$_2$Cu$_3$SnF$_{12}$, which has a distorted kagome lattice accompanied by four sorts of nearest-neighbor exchange interaction, has a disordered ground state described by a pinwheel valence-bond-solid state. The other parent compound, Cs$_2$Cu$_3$SnF$_{12}$, which has a uniform kagome lattice at room temperature, has an ordered gro…
We report the observation of magnetic domains in the exotic, antiferromagnetically ordered all-in-all-out state of Nd$_2$Zr$_2$O$_7$, induced by spin canting. The all-in-all-out state can be realized by Ising-like spins on a pyrochlore lattice and is established in Nd$_2$Zr$_2$O$_7$ below 0.31 K for external magnetic fields up to 0.14 T. Two different spin arrangements can fulfill this configuration which leads to the possibility of magnetic domains. The all-in-all-out domain structure can be controlled by an external magnetic field applied parallel to the [111] direction. This is a result of …
Antiferromagnetic to ferromagnetic phase transition as a transition to partial ordered spins. Application to $La_{1-x}Ca_xMnO_3$ in the doping range $x\geq 0.50$
Direction-dependent anisotropic exchange is a common feature of magnetic systems with strong spin-orbit coupling. Here we study the effect of such exchange upon macroscopic magnetic anisotropy for a face-centered-cubic model. By several theoretical techniques, we show that, both in the paramagnetic and ordered phases, the magnetic anisotropy is induced by fluctuations. Moreover, the magnetic anisotropy differs in the paramagnetic and ordered phases: in the paramagnetic phase the susceptibility is maximum along the $\langle111\rangle$ directions, while the magnetic moments orient along $\langle…
Three different tensor network optimization algorithms are employed to accurately determine the ground state and thermodynamic properties of the spin-3/2 kagome Heisenberg antiferromagnet. We found that the $\sqrt{3} \times \sqrt{3}$ state, rather than the $q = 0$ state, is the ground state of this system, and such an ordered state is melted at any finite temperature, thereby clarifying the existing experimental controversies. A 1/3-magnetization plateau in the magnetic curve is observed, being consistent with the experimental observation. The absence of a zero-magnetization plateau indicates …
We use Schwinger boson mean field theory (SBMFT) to study the ground state of the spin-$S$ triangular-lattice Heisenberg model with nearest ($J_1$) and next-nearest ($J_2$) neighbor antiferromagnetic interactions. Previous work on the $S=1/2$ model leads us to consider two spin liquid Ansätze, one symmetric and one nematic, which upon spinon condensation give magnetically ordered states with 120$^{\circ}$ order and collinear stripe order, respectively. The SBMFT contains the parameter $κ$, the expectation value of the number of bosons per site, which in the exact theory equals $2S$. For $κ=1$ …
Vanishing ordered moment in the frustrated triangular lattice antiferromagnet CuNdO$_2$
NIST Center for Neutron Research, National Institute of Standards and Technology（美国国家标准与技术研究院）；Department of Materials Science and Eng., University of Maryland（马里兰大学材料科学与工程系）；Stewart Blusson Quantum Matter Institute, University of British Columbia（不列颠哥伦比亚大学斯图尔特·布卢森量子物质研究所）；Laboratory for Solid State Physics, ETH Zurich（苏黎世联邦理工学院固体物理实验室）；Department of Physics, University of Toronto（多伦多大学物理系）；PSI Center for Neutron and Muon Sciences（瑞士保罗谢勒研究所中子与μ子科学中心）；Neutron Scattering Division, Oak Ridge National Laboratory（橡树岭国家实验室中子散射部）；Canadian Institute for Advanced Research (CIFAR)（加拿大高等研究院）
Suppression of the tendency toward antiferromagnetic order in the Dirac semimetal SrIrO$_3$
ShanghaiTech University（上海科技大学）；Westlake University（西湖大学）；Argonne National Laboratory（阿贡国家实验室）；University of Science and Technology of China（中国科学技术大学）；Zhengzhou University（郑州大学）；Henan Academy of Sciences（河南省科学院）
We study magnetic properties in the half-filled Hubbard model on the Ammann-Beenker tiling. First, we focus on the domain structure with locally eightfold rotational symmetry to examine the strictly localized confined states for the tightbinding model. We count the number of vertices and confined states in the larger domains generated by the deflation operations systematically. Then, the fraction of the confined states, which plays an important role for magnetic properties in the weak coupling limit, is obtained as $p=1/2τ^2$, where $τ(=1+\sqrt{2})$ is the silver ratio. It is also found that t…
Specific heat and magnetization measurements of the compound [Cu2(apyhist)2Cl2](ClO4)2, where apyhist = (4-imidazolyl)ethylene-2-amino-1-ethylpyridine), were used to identify a magnetic-field-induced long-range antiferromagnetic ordered phase at low temperatures (T < 0.36 K) and magnetic fields (1.6 T < H < 5.3 T). This system consists of a Schiff base copper(II) complex, containing chloro-bridges between adjacent copper ions in a dinuclear arrangement, with an antiferromagnetic intradimer interaction |Jintra|/kB = 3.65 K linked by an antiferromagnetic coupling |Jinter|z/kB = 2.7 K. The magnet…
