The magnetic and thermodynamic properties of spin-1/2 Heisenberg diamond chains are investigated in three different cases: (a) J1, J2, J3>0 (frustrated); (b) J1, J3<0, J2>0 (frustrated); and (c) J1, J2>0, J3<0 (non-frustrated). The density matrix renormalization group (DMRG) technique is invoked to study the properties of the system in the ground state, while the transfer matrix renormalization group (TMRG) technique is applied to explore the thermodynamic properties. The local magnetic moments, spin correlation functions, and static structure factors are discussed in the ground state for the three cases. It is shown that the static structure factor S(q) shows peaks at wavevectors $q=aπ/3$ (a=0,1,2,3,4,5) for different couplings in a zero magnetic field, which, however in the magnetic fields where the magnetization plateau with m=1/6 pertains, exhibits the peaks only at q=0, $2π/3$ and $4π/3$, which are found to be couplings-independent. The DMRG results of the zero-field static structure factor can be nicely fitted by a linear superposition of six modes, where two fitting equations are proposed. It is observed that the six modes are closely related to the low-lying excitations of the system. At finite temperatures, the double-peak structures of the susceptibility and specific heat against temperature are obtained, where the peak positions and heights are found to depend on the competition of the couplings. It is also uncovered that the XXZ anisotropy of F and AF couplings leads the system of case (c) to display quite different behaviors. In addition, the experimental data of the susceptibility, specific heat and magnetization for the compound Cu$_{3}$(CO$_{3}$)$_{2}$(OH)$_{2}$ are fairly compared with our TMRG results.
The magnetic Ln$^{3+}$ ions in the fergusonite and scheelite crystal structures form a distorted or stretched diamond lattice which is predicted to host exotic magnetic ground states. In this study, polycrystalline samples of the fergusonite orthotantalates $M$-LnTaO$_4$ (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) are synthesized and then characterized using powder diffraction and bulk magnetometry and heat capacity. TbTaO$_4$ orders antiferromagnetically at 2.25 K into a commensurate magnetic cell with $\vec{k}=0$, magnetic space group 14.77 ($P2_1$$'/c$) and Tb moments parallel to the $a$-axis. No…
To study non-Heisenberg effects in the vicinity of spin crossover in strongly correlated electron systems we derive an effective low-energy Hamiltonian for the two-band Kanamori model. It contains Heisenberg high-spin term proportional to exchange constant as well as low-spin term proportional to spin gap parameter $\varepsilon_s$. Using cluster mean field theory we obtain several non-Heisenberg effects. Near critical value of spin gap $\varepsilon^c_s$ there is a magnetic phase transition of first order. In the vicinity of $\varepsilon^c_s$ in the paramagnetic phase we observe non trivial beh…
Direct observation of impurity-induced magnetism in an S = 1/2 antiferromagnetic Heisenberg 2-leg spin ladder
采用核磁共振和磁化强度测量方法研究了Bi（Cu（1-x）Znx）2 PO 6（0<x 0）的磁性特征<0.05 at temperatures between 2.6 K and 300 K. The simple lineshape of the 31P NMR signals of the pristine compound changes considerably for x>，发现Zn位附近的局部磁化强度随温度变化.采用QMC方法对有限尺寸的适当自旋系统进行模型计算的结果表明了这种观察的一般性质。
Magnetism of Cu_6 Ge_6 O_{18}-x H_2 O (x = 0 ~ 6), a compound of the one-dimensional Heisenberg $S = 1/2$ model with competing antiferromagnetic interactions
我们测量了Cu $_6$ Ge $_6$ O $_{18}$ -xH $_2$ O（$x = 0 \sim 6$）的磁化率.反铁磁（AF）转变温度（$T_{\rm N}$）以上的磁化率同意与竞争AF相互作用的一维海森堡$S = 1/2$模型的磁化率。从最近邻和次最近邻AF交换相互作用之间的估计比率，自旋系统可能位于具有无隙和有隙磁激发的自旋系统之间的边界附近。$T_{\rm N}/T_{\rm max}$的值（其中$T_{\rm max}$是磁化率最大时的温度）显示出对$x$的独特依赖性。$x$依赖性可以定性地解释作为$x$的函数的相变和无序的影响考虑。
The spin-1/2 Heisenberg antiferromagnet on the frustrated diamond-decorated square lattice is known to feature various zero-field ground-state phases, consisting of extended monomer-dimer and dimer-tetramer ground states as well as a ferrimagnetic regime. Using a combination of analytical arguments, density matrix renormalization group (DMRG), exact diagonalization, as well as sign-problem-free quantum Monte Carlo (QMC) calculations, we investigate the properties of this system and the related Lieb lattice in the presence of a finite magnetic field, addressing both the ground-state phase diagr…
We investigate the magnetic properties of LiYbO$_2$, containing a three-dimensionally frustrated, diamond-like lattice via neutron scattering, magnetization, and heat capacity measurements. The stretched diamond network of Yb$^{3+}$ ions in LiYbO$_2$ enters a long-range incommensurate, helical state with an ordering wave vector ${\bf{k}} = (0.384, \pm 0.384, 0)$ that "locks-in" to a commensurate ${\bf{k}} = (1/3, \pm 1/3, 0)$ phase under the application of a magnetic field. The spiral magnetic ground state of LiYbO$_2$ can be understood in the framework of a Heisenberg $J_1-J_2$ Hamiltonian on…
Ground-state phase diagrams and magnetization curves of a spin-1 Heisenberg diamond cluster with two different coupling constants and uniaxial single-ion anisotropy are investigated in a presence of the external magnetic field with the help of exact diagonalization methods. It is shown that the spin-1 Heisenberg diamond cluster exhibits several remarkable quantum ground states, which are manifested in zero- and low-temperature magnetization curves as intermediate plateaus at one-quarter, one-half and three-quarters of the saturation magnetization. It is found that the width of the fractional m…
This work reports the synthesis, structure and magnetic properties of the single crystal of a facile spin 1/2 one dimensional Heisenberg antiferromagnet bis(4-aminopyridinium) bis(oxalato)cuprate(II) dihydrate, (C 5 H 7 N 2 ) 2 [Cu(C 2 O 4 ) 2 ].2H 2 O. Single crystals of large sizes of the title compound were obtained using the technique of liquid-liquid diffusion or layer diffusion with 100 % yield. Single crystal X-ray diffraction measurements revealed a very good quality of the grown single crystals with small value of goodness of fit R obtained at 1.058. The structure comprises corner-sha…
Spin order and dynamics in the diamond-lattice Heisenberg antiferromagnets CuRh2O4 and CoRh2O4
金刚石晶格上的反铁磁绝缘体是具有奇异磁现象的候选材料，从自旋轨道纠缠到简并螺旋基态和拓扑顺磁性。相对于其他三维磁性离子网络，如几何阻挫烧绿石晶格，金刚石晶格磁性在实际材料中的研究还不成熟。在这项工作中，我们通过热磁和中子散射测量来表征模型A位尖晶石CoRh 2 O 4（钴蔷薇辉石）和CuRh 2 O 4（铜蔷薇辉石）的磁性，并进行群论分析，Rietveld精化，平均场论和自旋波理论计算来分析实验结果。我们的研究表明，立方CoRh_2 O_4是一个典型的S=3/2金刚石晶格Heisenberg反铁磁体，最近邻交换J = 0.63meV，在25 K以下为Neel有序基态。在四边形扭曲CuRh 2 O 4中，第三近邻自旋之间的竞争交换相互作用导致在24 K下出现无公度自旋螺旋，其磁传播矢量k =（0，0，0.79）.强减少的有序矩观察到的S=1/2自旋CuRh 2 O 4和捕获我们的1/S校正交错磁化。我们的工作确定CoRh 2 O 4和CuRh 2 O 4作为参考材料，以指导未来的工作寻找奇异的量子行为在金刚石晶格反铁磁体。
结果表明，重电子的巡游局域跃迁发生在近藤-海森堡晶格的磁有序相内。用连续时间量子蒙特卡罗方法结合动力学平均场论导出了相图和电子结构。在巡游局域化跃迁附近，费米面上出现了几乎平坦的带，准粒子重整化因子几乎为零。与此同时，出现了一个能量尺度很小的强局域磁涨落。考虑到反铁磁和铁磁海森堡相互作用，在CeRh $_{1-x}$ Co $_x$ In $_5$，CeRu $_2$（Si $_x$ Ge $_{1-x}$）$_2$，UGe $_2$和CeT $_2$ Al $_{10}$（T=Fe，Ru，Os）中观察到的丰富相图上实现了一致的理解。
Spin-1/2 Heisenberg diamond-like decorated honeycomb lattice in a magnetic field from the perspective of localized magnons and exact diagonalization
Faculty of Science, P. J. Šafárik University（帕·约·沙法里克大学理学院）；Laboratoire de Physique Théorique et Modélisation, CNRS UMR 8089, CY Cergy Paris Université（CY塞尔吉巴黎大学，CNRS UMR 8089理论物理与建模实验室）
Thermal first-order phase transitions, Ising critical points, and reentrance in the Ising-Heisenberg model on the diamond-decorated square lattice in a magnetic field
Magnetization plateaus, spin-canted orders and field-induced transitions in a spin-1/2 Heisenberg antiferromagnet on a distorted diamond-decorated honeycomb lattice
Institute of Physics, Faculty of Science, P. J. Šafárik University（帕日·沙法里克大学理学院物理研究所）
Frustrated quantum magnets may exhibit fascinating collective phenomena. The main goal of this dissertation is to provide conclusive evidence for the emergence of novel phases of matter like quantum spin liquids in local quantum spin models. We develop novel algorithms for large-scale Exact Diagonalization computations. Sublattice coding methods for efficient use of lattice symmetries in the procedure of diagonalizing the Hamiltonian matrix are proposed and suggest a randomized distributed memory parallelization strategy. Benchmarks of computations on various supercomputers with system size up…
Spin dependent impurity effects in the 2D frustrated magnetism of NiGa$_2$S$_4$
研究了杂质对三角形反铁磁体Ni $_{1-x}M_x$ Ga $_2$ S $_4$（$M=$ Mn、Fe、Co和Zn）的影响。二维冻结自旋无序态的NiGa $_2$ S $_4$对Zn $^{2+}$（$S=0$）和Heisenberg Fe $^{2+}$（$S=2$）自旋的取代是稳定的，并表现出$T^2$依赖的磁比热，由外斯温度标度。相反，用具有Ising样各向异性的Co $^{2+}$（$S=3/2$）自旋和Heisenberg Mn $^{2+}$（$S=5/2$）自旋取代诱导常规自旋玻璃相。从这些比较中，它表明，海森堡自旋的整数大小是重要的，以稳定在冻结自旋无序态中观察到的二维相干行为。
Static and Dynamic Magnetic Properties of Spin-1/2 Inequilateral Diamond-Chain Compounds $A_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ ($A$=K, Rb, and Cs)
自旋为1/2的化合物A3 Cu 3AlO 2（SO 4）4（A=K，Rb，Cs）具有一维不等边金刚石链。我们分析了磁化率的温度依赖性，并确定磁交换相互作用。与蓝铜矿相反，二聚体形成在金刚石的一侧。通过对模型的数值分析，我们发现二聚体和一个近似孤立的一维海森堡链共同表征了磁性，包括磁化曲线和磁激发。这意味着，没有挫折的二聚体-单体复合物链是描述这些化合物的良好起点。
Magnetism and spin dynamics of Na$_5$Yb(MoO$_4$)$_4$: A weakly interacting rare-earth stretched diamond lattice
National Taiwan University（国立台湾大学）；Academia Sinica（中央研究院）；Sungkyunkwan University（成均馆大学）；KEK（高能加速器研究机构）；National Tsing Hua University（国立清华大学）；National Synchrotron Radiation Research Center（国家同步辐射研究中心）；University of Johannesburg（约翰内斯堡大学）
The existence and stability of spin-liquid phases represent a central topic in the field of frustrated magnetism. While a few examples of spin-liquid ground states are well established in specific models (e.g. the Kitaev model on the honeycomb lattice), recent investigations have suggested the possibility of their appearance in several Heisenberg-like models on frustrated lattices. An important related question concerns the stability of spin liquids in the presence of small perturbations in the Hamiltonian. In this respect, the magnetoelastic interaction between spins and phonons represents a …
We report the crystal structures and magnetic properties of two psuedo-polymorphs of the $S=1/2$ Ti$^{3+}$ coordination framework, KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O. Single-crystal X-ray and powder neutron diffraction measurements on $α$-KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O confirm its structure in the tetragonal $I4/mcm$ space group with a square planar arrangement of Ti$^{3+}$ ions. Magnetometry and specific heat measurements reveal weak antiferromagnetic interactions, with $J_1\approx7$ K and $J_2/J_1=0.11$ indicating a slight frustration of nearest- and next-nearest-neighbor interactions. Below $…
