Crystal and magnetic structures of a series of novel quantum spin trimer system Ca3Cu3xNix(PO4)4 (x=0,1,2) were studied by neutron powder diffraction at the temperatures 1.5-290 K. The composition with one Ni per trimer (x=1) has a monoclinic structure (space group P 21 /a, no. 14) with the unit cell parameters a = 17.71 A, b = 4.89 A, c = 8.85 A and = 123.84 deg at T=290 K. The (x=2) composition crystallizes in the C 2/c space group (no. 15) with the doubled unit cell along c-axis. Each trimer is formed by two crystallographic positions: one in the middle and the second one at the ends of the trimer. We have found that the middle position is occupied by the Cu2+, whereas the end positions are equally populated with the Cu2+ and Ni2+ for (x=1) while in the (x=2) the trimers were found to be of only one type Ni-Cu-Ni. Below TN = 20 K the (x=2) compound shows an antiferromagnetic ordering with propagation vector star {[1/2,1/2, 0], [-1/2,1/2, 0]} The magnetic structure is very well described with the irreducible representation tau22 using both arms of the star {k} with the magnetic moments 1.89(1) muB and 0.62(2) muB for Ni2+ and Cu2+ ions, respectively. We note that our powder diffraction data cannot be fitted by a model containing only one arm of the propagation vector star. The Cu/Ni-spins form both parallel and antiparallel configurations in the different trimers, implying substantial effect of the inter-trimer interaction on the overall magnetic structure.
Spin-1 antiferromagnets are abundant in nature, but few theories or results exist to understand their general properties and behavior, particularly in situations when geometric frustration is present. Here we study the $S=1$ Kagome compound Na$_2$Ti$_3$Cl$_8$ using a combination of Density Functional Theory, Exact Diagonalization, and Density Matrix Renormalization Group methods to achieve a first principles supported explanation of exotic magnetic phases in this compound. We find that the effective magnetic Hamiltonian includes essential non-Heisenberg terms that do not stem from spin-orbit c…
Doping-induced spin-manipulation in complex trimer system Ca$_{3}$Cu$_{3}$(PO$_{4}$)$_{4}$: A First Principles Study
用磁性（Ni）和非磁性（Mg）掺杂剂进行自旋操纵掺杂构成了从具有双重基态的线性链海森堡反铁磁Cu基$d^{9}$自旋1/2三聚体化合物Ca $_{3}$ Cu $_{3}$（PO $_{4}$）$_{4}$获得单重态基态系统的实验尝试。本研究是基于第一性原理的调查，这种掺杂的自旋交换机制和电子结构的母体化合物的影响。在获得具有单重态基态的自旋带隙系统方面，用零自旋掺杂剂（如Mg）的位置选择性掺杂被证明比整体自旋掺杂剂Ni更有效，如在实验研究中也观察到的。掺杂诱导的二聚态的基态能量最低。计算出的自旋交换值沿各种可能的路径很好地与早期的实验结果相似。
Since the discovery of the Verwey transition in magnetite, transition metal compounds with pyrochlore structures have been intensively studied as a platform for realizing remarkable electronic phase transitions. We report the discovery of a unique phase transition that preserves the cubic symmetry of the beta-pyrochlore oxide CsW$_2$O$_6$, where each of W 5d electrons are confined in regular-triangle W3 trimers. This trimer formation is an unprecedented self-organization of d electrons, which can be resolved into a charge order satisfying the Anderson condition in a nontrivial way, orbital ord…
The wavefuntion of conduction electrons moving in the background of a non-coplanar spin structure can gain a quantal phase - Berry phase - as if the electrons were moving in a strong fictitious magnetic field. Such an emergent magnetic field effect is approximately proportional to the solid angle subtended by the spin moments on three neighbouring spin sites, termed the scalar spin chirality. The entire spin chirality of the crystal, unless macroscopically canceled, causes the geometrical Hall effect of real-space Berry-phase origin, whereas the intrinsic anomalous Hall effect (AHE) in a conve…
Recent experiments have reported that inserting metal atoms or small molecules in between the FeSe layers of $β$-FeSe can significantly enhance the superconducting transition temperature. Here, based on first-principles electronic structure calculations, we propose a stable compound SnOFeSe by alternatively stacking the SnO and $β$-FeSe layers. The predicted SnOFeSe has the same tetragonal structure as the well-known FeAs-based compound LaOFeAs, meanwhile their electronic structures in the nonmagnetic state are quite similar. The magnetic ground state of SnOFeSe is predicted to be the dimer an…
We carried out a comprehensive study of magnetic critical behavior in single crystals of ternary chalcogenide FeCr$_2$Te$_4$ that undergoes a ferrimagnetic transition below $T_c$ $\sim$ 123 K. Detailed critical behavior analysis and scaled magnetic entropy change indicate a second-order ferrimagentic transition. Critical exponents $β= 0.30(1)$ with $T_c = 122.4(5)$ K, $γ= 1.22(1)$ with $T_c = 122.8(1)$ K, and $δ= 4.24(2)$ at $T_c$ $\sim$ 123 K suggest that the spins approach three-dimensional Ising ($β$ = 0.325, $γ$ = 1.24, and $δ$ = 4.82) model coupled with the attractive long-range interacti…
Designing electronic magnetoelectric matter with organic quantum spin trimers
Osaka Metropolitan University（大阪公立大学）；University of Florida（佛罗里达大学）；Shanghai Jiao Tong University（上海交通大学）；Osaka Prefecture University（大阪府立大学）；Florida State University（佛罗里达州立大学）；National High Magnetic Field Laboratory, Florida State University（佛罗里达州立大学国家高磁场实验室）
In this study, we systematically study on crystal and electronic structures and optical absorption properties of perfect monolayer MoS2 (M), M with S vacancy (M@SV), M with N doping at S site (M@ND) and M with both S vacancy and N doping at S site (M@V-D) using first-principles method. It is showed that the N atom is tend to located between Mo and S layers, leaving one vacancy at original site, to form interstitial N atom. Thus, the interstitial N atom and the S vacancy make up the NI-VS dimer. We study M@V-D with five atomic configurations and find the most stable structure having the NI-VS-V…
Melting temperatures at ambient pressure of systems of isosceles Lennard-Jones trimers with angles ranging from 70 degrees to 100 degrees are determined. Two crystal structures are considered: a distorted body centered cubic structure and a distorted face centered cubic structure with preferred angles of 77 and 96 degrees, respectively. Liquid dynamics are slowed down when the angle is increased. A trimer angle of 83 degrees yields the largest distance between isochrones and the melting temperature, suggesting that this value gives the optimal glass-forming ability. It is conjectured that bett…
Anisotropic physical properties of PrRhAl$_4$Si$_2$ single crystal a non-magnetic singlet ground state compound
我们已经生长出PrRhAl $_4$ Si $_2$的单晶，其以四方晶体结构结晶。从低温物理性质的测量，如，磁化率，磁化强度，热容和电阻率，我们发现，该化合物不显示任何磁有序低至70 mK。通过对样品磁化率和比热测量的晶场计算表明，PrRhAl $_4$ Si $_2$中Pr原子的9重简并$(2J+1)$能级在123 K处分裂为7个能级，其中有一个单重态基态和一个分离良好的激发二重态，总能级分裂能为320 K.
We report optimized crystal growth conditions for the quarternary compound AgCrP$_2$S$_6$ by chemical vapor transport. Compositional and structural characterization of the obtained crystals were carried out by means of energy-dispersive X-ray spectroscopy and powder X-ray diffraction. AgCrP$_2$S$_6$ is structurally closely related to the $M_2$P$_2$S$_6$ family, which contains several compounds that are under investigation as 2D magnets. As-grown crystals exhibit a plate-like, layered morphology as well as a hexagonal habitus. AgCrP$_2$S$_6$ crystallizes in monoclinic symmetry in the space grou…
Herein, we report the discovery of a novel Gd-based magnetic compound GdPt$_2$B with a chiral crystal structure. X-ray diffraction and chemical composition analyses reveal a CePt$_2$B-type crystal structure (space group: $P6_422$) for GdPt$_2$B. Moreover, we successfully grew single crystals of GdPt$_2$B using the Czochralski method. Magnetization measurements and the Curie$-$Weiss analysis demonstrate that the ferromagnetic interaction is dominant in GdPt$_2$B. A clear transition is observed in the temperature dependence of electrical resistivity, magnetic susceptibility, and specific heat at…
Motivated by fine tuning of the magnetic and topological properties of MnBi$_2$Te$_4$ via defect engineering, in this work, we report the crystal growth of MnBi$_2$Te$_4$ and related compounds using vapor transport method and characterization of vapor transported crystals by measuring elemental analysis, magnetic and transport properties, and scanning tunneling microscopy. For the growth of MnBi$_2$Te$_4$ single crystals, I$_2$, MnI$_2$ , MnCl$_2$, TeCl$_4$, or MoCl$_5$ are all effective transport agents; chemical transportation occurs faster in the presence of iodides than chlorides. MnBi$_2$…
Barium ruthenate Ba$_{4}$Ru$_{3}$O$_{10}$, in which Ru$_{3}$O$_{12}$ trimers are connected together to form a chequered two-dimensional framework, has been synthesised and its structural, magnetic and transport properties studied between 300 K and 2 K. The paramagnetic to antiferromagnetic transition at $T_N \sim 105$ K evidenced on the susceptibility curve coincides with an increase of electron localization in transport measurements. Thermoelectric power and Hall coefficient measurements both exhibit dramatic changes at $T_N$, characteristic of a reconstruction of the bands structure near the…
The single ion properties of the zig-zag chain compound SrTm$_2$O$_4$ have been investigated using heat capacity, magnetic susceptibility, magnetization, inelastic neutron scattering, and polarized muon spectroscopy. Two crystal field models are employed to estimate the single ion properties; a Density Function Theory based model and an effective charge model based on the Hutchings point charge model. The latter describes our experimental results well. This model estimates an easy-axis anisotropy for one of the Tm$^{3+}$ sites and an easy-plane anisotropy for the second site. It also predicts …
Crystal structure, magnetism, and bonding of the hexagonal compounds Pd$_{1.63}$Mn$_{0.37}$Si and Pd$_{1.82}$Mn$_{0.18}$Ge related to the Fe$_2$P structure
Recent attempts at topological materials have revealed a large class of materials that show gapless surface states protected by time-reversal symmetry and crystal symmetries. Among them, topological insulating states protected by crystal symmetries, rather than time-reversal symmetry are classified as topological crystalline insulators. We computationally predict the signature of new three-dimensional topological crystalline insulating compounds of space group 139(I/4mmm). After conducting a full volume optimization process by allowing to rearrange of atomic positions and lattice parameters, t…
Based on the relativistic spin-polarized density functional theory calculations we investigate the crystal structure, electronic and magnetic properties of a family MnPn2Ch4 compounds, where pnictogen metal atoms (Pn) are Sb and Bi; chalcogens (Ch) are Se, Te. We show that in the series the compounds of this family with heavier elements prefer to adopt rhombohedral crystal structure composed of weakly bonded septuple monoatomic layers while those with lighter elements tend to be in the monoclinic structure. Irrespective of the crystal structure all compounds of the MnPn2Ch4 series demonstrate …
We successfully grew single crystals of Si- and Ge-square-net compounds of NbSiSb and NbGeSb whose excellent crystalline quality are verified using single-crystal x-ray diffraction, rocking curves, scanning and transmission electron microscopies. Since these two compounds share major crystallographic similarity with the topological nodal-line semimetals of ZrSiS family, we employ density functional theory (DFT) calculations and magnetotransport measurements to demonstrate their band structures as well as the electron scattering mechanisms. DFT calculations show that the fermiology shows strong…
In this study, we present a novel approach along with the needed computational strategies for efficient and scalable feature engineering of the crystal structure in compounds of different chemical compositions. This approach utilizes a versatile and extensible framework for the quantification of a three-dimensional (3-D) voxelized crystal structure in the form of 2-point spatial correlations of multiple atomic attributes and performs principal component analysis to extract the low-dimensional features that could be used to build surrogate models for material properties of interest. An applicat…
Anthracene derivative compounds are currently investigated because of their unique physical properties (e.g., bright luminescence and emission tunability), which make them ideal candidates for advanced optoelectronic devices. Intermolecular interactions are the basis of the tunability of the optical and electronic properties of these compounds, whose prediction and exploitation benefit from the knowledge of the crystal structure and the packing architecture. Polymorphism can occur due to the weak intermolecular interactions, asking for detailed structural analysis clarifying the origin of obse…
To accelerate development of innovative materials, their modelings and predictions with useful functionalities are of vital importance. Here, based on a recently developed crystal structure prediction method, we find a new family of stable two-dimensional crystals with an open-channel tetrahedral bonding network, rendering a potential for electronic and energy applications. The proposed structural prototype with a space group of Cmme hosts at least thirteen different freestanding T$_{3}$X compounds with group IV (T=C, Si, Ge, Sn) and VI (X=O, S, Se, Te) elements. Moreover, the proposed materia…
We analyze the anisotropic electrical and thermal transport measurements in single crystals of In2Te5 belonging to monoclinic space group C12 c1 with the temperature gradient applied parallel and perpendicular to the crystallographic c-axis of the crystals. The thermal conductivity along the c-axis thermal conductivity parallel was found to smaller by a factor of 2 compared to the thermal conductivity along the direction perpendicular to the c-axis over the entire temperature range. In contrast, the Seebeck coefficient along the c-axis parallel was found to be higher than its value along the d…
Polycrystalline Ba4NbIr3O12 has recently been shown to be a promising spin liquid candidate. We report an easy and reliable method to grow millimeter-sized single crystals of this trimer based spin liquid candidate material with the actual stoichiometry of Ba4Nb0.8Ir3.2O12. The growth of large crystals is achieved using BaCl2 as flux. The crystals show hexagonal plate-like habit with edges up to 3 mm in length. The structure is confirmed by single crystal X-ray diffraction and is found to be the same as of previously reported phase Ba12Nb2.4Ir9.6O36 [Ba4Nb0.8Ir3.2O12], indeed with a mixed occu…
The fundamental principles underlying the arrangement of elements into solid compounds with an enormous variety of crystal structures are still largely unknown. This study presents a general overview of the structure types appearing in an important subset of the solid compounds, i.e., binary and ternary compounds of the 6A column oxides, sulfides and selenides. It contains an analysis of these compounds, including the prevalence of various structure types, their symmetry properties, compositions, stoichiometries and unit cell sizes. It is found that these compound families include preferred st…
Absence of a Competition between Magnetism and Superconductivity in the Layered Nickel Borocarbides: Common Correlation Tc with Crystal Chemical Parameters for Magnetic and Nonmagnetic Compounds
In the multiferroic hexagonal manganite HoMnO3, inelastic neutron scattering and synchrotron based THz spectroscopy have been used to investigate the spin waves associated to the Mn order together with Ho crystal field excitations. While the Mn order sets in first below 80 K, a spin reorientation occurs below 37 K, a rare feature in the rare earth manganites. We show that severalHo crystal field excitations are present in the same energy range as the magnons, and that they are all affected by the spin reorientation. Moreover, several anomalous features are observed in the excitations at low te…
Materials with tunable topological features, simple crystal structure and flexible synthesis, are in extraordinary demand towards technological exploitation of unique properties of topological nodal points. The controlled design of the lattice geometry of light elements is determined by utilizing density functional theory and the effective Hamiltonian model together with the symmetry analysis. This provides an intriguing venue for reasonably achieving various distinct types of novel fermions. We, therefore, show that a nodal line (type-I and II), Dirac fermion, and triple point (TP) fermionic …
New intercalation compounds Cr$_x$ZrTe$_2$ were synthesized in the Cr concentration range of x=0-0.3. A thorough study of the crystal and electronic structure has been performed. It was found that there is competition in the distribution of the Cr atoms over the octa- and tetrahedral sites in the van der Waals gap, depending on the Cr content. The ordering of the Cr atoms was found at x = 0.25; at the same time, the lattice symmetry decreases from trigonal P-3m1 to monoclinic F2/m. This ordering stabilizes the octahedral coordination of the Cr atoms by Te atoms. The analysis of the experimenta…
