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A new frustrated spin-cluster antiferromagnet Sr2Co3(C2O4)3(OH)4·3H2O has been synthesized by the hydrothermal method. The basic magnetic unit of this compound is an isolated Co6 cluster, which is ...

We have grown single crystals of ${\mathrm{Na}}_{2}\mathrm{BaNi}{({\mathrm{PO}}_{4})}_{2}$, a spin-1 equilateral triangular lattice antiferromagnet (ETLAF), and performed magnetic susceptibility, specific heat, and thermal conductivity measurements at ultralow temperatures. The main results are as follows: (i) At zero magnetic field, ${\mathrm{Na}}_{2}\mathrm{BaNi}{({\mathrm{PO}}_{4})}_{2}$ exhibits a magnetic ordering at 430 mK with a weak ferromagnetic moment along the $c$ axis. This suggests a canted ${120}^{\ensuremath{\circ}}$ spin structure, which is in a plane including the crystallographic $c$ axis due to the existence of an easy-axis anisotropy and ferromagnetically stacked along the $c$ axis. (ii) With increasing field along the $c$ axis, a 1/3 magnetization plateau is observed, which means that the canted ${120}^{\ensuremath{\circ}}$ spin structure is transformed into an up-up-down (UUD) spin structure. With even higher fields, the UUD phase further evolves into possible V and ${\mathrm{V}}^{\ensuremath{'}}$ phases. (iii) With increasing field along the $a$ axis, the canted ${120}^{\ensuremath{\circ}}$ spin structure is possibly transformed into an umbrella phase and a V phase. Therefore ${\mathrm{Na}}_{2}\mathrm{BaNi}{({\mathrm{PO}}_{4})}_{2}$ is a rare example of a spin-1 ETLAF with single-crystalline form that exhibits easy-axis spin anisotropy and a series of quantum spin state transitions.

We have synthesized a new spin-1/2 antiferromagnet, Y2Cu7(TeO3)6Cl6(OH)2, via a traditional hydrothermal method. This compound crystallizes in the triclinic crystal system with space group P1. The magnetic ions constitute a two-dimensional layered lattice with a novel topological structure in which the Cu4 clusters make up distorted diamond chains along the a axis and these chains are connected by the Cu3 trimers. The magnetic susceptibility and specific heat measurements show that the compound is antiferromagnetically ordered at TN = 4.1 K. This antiferromagnetic ordering is further supported by electron spin resonance (ESR) data. The magnetization curve presents a field-induced metamagnetic transition at 0.2 T, followed by a magnetization plateau within a wide magnetic field range from 7 T to at least 55 T, which corresponds to 3/7 of the saturated magnetization with g = 2.15 obtained from ESR. The possible mechanism for the magnetization plateau is discussed.

Single crystal Na2Co2TeO6 has been successfully grown by self-flux method, and its lattice structure and basic magnetic properties were characterized. As determined by single crystal X-ray diffraction, Na2Co2TeO6 belongs to space group P6322 (182) with a = b = 5.2709(2) A, c = 11.2615(15) A, and V = 270.95 (4) A3, the crystal structure is a layered honeycomb formed by CoO6 octahedra and the TeO6 octahedra in the center of the honeycomb layers, and the NaO6 octahedra are between the honeycomb layers. Magnetic susceptibility measurements indicate that the single crystal sample displays a distinct anisotropic behavior and the spin parallels the honeycomb plane (ab-plane). In a lower temperature region, a series of antiferromagnetic-like (AFM-like) phase transitions were observed, which may result from the spin reorientation of Co2+ ions. The different magnetization behavior between the polycrystalline structure and the single crystal (with the magnetic field parallel to and perpendicular to the ab-plane) rev...

In low-dimensional Ising spin systems, an interesting observation is the presence of step magnetization at low temperatures. Here we combine both DC and pulsed magnetic fields to study the 1/3 magnetization plateau and multiple steps in the Ising spin-chain material α-CoV

A recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state. The ultimate question is whether the QSL survives disorder or the disorder leads to a "spin-liquid-like" state, such as the proposed random-singlet (RS) state. Since disorder is a standard feature of most QSL candidates, this question represents a major challenge for QSL candidates. YbMgGaO$_4$, a triangular lattice antiferromagnet with effective spin-1/2 Yb$^{3+}$ ions, is an ideal system to address this question, since it shows no long-range magnetic ordering with Mg/Ga site disorder. Despite the intensive study, it remains unresolved as to whether YbMgGaO$_4$ is a QSL or in the RS state. Here, through ultralow-temperature thermal conductivity and magnetic torque measurements, plus specific heat and DC magnetization data, we observed a residual $\kappa_0/T$ term and series of quantum spin state transitions in the zero temperature limit for YbMgGaO$_4$. These observations strongly suggest that a QSL state with itinerant excitations and quantum spin fluctuations survives disorder in YbMgGaO$_4$., Comment: 31 pages, 10 figures

A recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state. The ultimate question is whether the QSL survives disorder or the disorder leads to a “spin-liquid-like” state, such as the proposed random-singlet (RS) state. Since disorder is a standard feature of most QSL candidates, this question represents a major challenge for QSL candidates. YbMgGaO4, a triangular lattice antiferromagnet with effective spin-1/2 Yb3+ions, is an ideal system to address this question, since it shows no long-range magnetic ordering with Mg/Ga site disorder. Despite the intensive study, it remains unresolved as to whether YbMgGaO4 is a QSL or in the RS state. Here, through ultralow-temperature thermal conductivity and magnetic torque measurements, plus specific heat and DC magnetization data, we observed a residual κ0/T term and series of quantum spin state transitions in the zero temperature limit for YbMgGaO4. These observations strongly suggest that a QSL state with itinerant excitations and quantum spin fluctuations survives disorder in YbMgGaO4., It remains an open question as to whether the quantum spin liquid state survives material disorder, or is replaced by some spin-liquid like state. Here, Rao et al succeed in resolving a resolving a κ0/T residual in the thermal conductivity of YbMgGaO4 strongly suggesting the survival of the quantum spin liquid state.

Rare-earth pyrochlores are known to exhibit exotic magnetic phenomena. We report a study of crystal growth and characterizations of a new rare-earth compound ${\mathrm{Er}}_{2}{\mathrm{AlSbO}}_{7}$, in which ${\mathrm{Al}}^{3+}$ and ${\mathrm{Sb}}^{5+}$ ions share the same positions with a random distribution. The magnetism is studied by magnetic susceptibility, specific heat, and thermal conductivity measurements at low temperatures down to several tens of millikelvin. Different from the other reported Er-based pyrochlores exhibiting distinct magnetically ordered states, a spin-freezing transition is detected in ${\mathrm{Er}}_{2}{\mathrm{AlSbO}}_{7}$ below 0.37 K, which is primarily ascribed to the inherent structural disorder. A cluster spin-glass state is proposed in view of the frequency dependence of the peak position in the ac susceptibility. In addition, the temperature and field dependence of thermal conductivity indicates rather strong spin fluctuations which is probably due to the phase competition.

We report crystal growth, magnetic properties and electron spin resonance (ESR) study of the one dimensional zigzag-chain compound FeNbO4. The single crystals were grown by the flux method using Na2WO4·12H2O and Na2W2O7 as the flux. Magnetic susceptibility and specific heat data show an antiferromagnetic ordering below 44 K. High-field magnetization data reveal a spin-flop transition at 12 T when magnetic field is applied along the magnetic easy axis. Multi-frequency ESR study on the single crystals reveal three resonance modes which can be understood by the molecule-field theory. Using a simple model with easy-axis type anisotropy, we estimate that the anisotropy field HA and the exchange field HE are 2.67 T and 27 T, respectively. The zero-frequency resonance field at 11 T corresponds to the spin-flop transition, demonstrating a close correlation between the high-field magnetization and the ESR spectra.

A new two-dimensional (2D) fluorophosphate compound Na3Cu5(PO4)4F·4H2O with a Cu5 cluster has been synthesized using a conventional hydrothermal method. The compound crystallizes in the orthorhombic crystal system with space group Pnma. The 2D layered structure is formed by cap-like {Cu5(PO4)4F} building units consisting of a Cu4O12F cluster plus a residual cap Cu2+ ion. Magnetic susceptibility exhibits a broad maximum at T2 = 19.2 K due to low-dimensional character followed by a long-range antiferromagnetic ordering at T1 = 11.5 K, which is further confirmed by the specific heat data. High-field magnetization measurement demonstrates a 2/5 quantum magnetization plateau above 40 T. The ESR data indicate the presence of magnetic anisotropy, in accordance with the 2D structure of the system.

Nanometer scale is introduced in the well-known Haldane system $$\hbox {Y}_{2}\hbox {BaNiO}_{5}\,(S=1)$$ . Magnetization and pulsed-field electron spin resonance (ESR) measurements were performed. As a result, the magnetization of nanoparticles is much enhanced as compared with that of the bulk material. The Haldane gap in the bulk form tends to be suppressed as the grain size is reduced down to the nanometer scale. The chain-end $$S\hbox {-}1/2$$ spins have an important contribution to the magnetism of nanoparticles. The high-field ESR data demonstrated a paramagnetic-like resonance. The frequency–field (f–H) relationship is linear and passes through the origin. The g value is about 2.16, in good agreement with the typical value of paramagnetic $$\hbox {Ni}^{2+}$$ . It is concluded that the nanometer scale is a new degree of freedom for controlling the ground state of quantum magnets.

We report anisotropic magnetization plateaus in the skew-chain antiferromagnet ${\mathrm{Co}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ with ${S}_{\mathrm{eff}}=1/2$ and a large $g$ factor. When the field is applied along the easy $b$ axis, a 1/2-like magnetization plateau is observed within $5.4\ensuremath{\sim}11.6\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, followed by a 3/4 plateau at 15.7 T. For the hard $a$ and $c$ axes, however, there is only a sign of 1/2-like magnetization plateau. These observations are quite different from the isostructural ${\mathrm{Ni}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ [Z. W. Ouyang et al., Phys. Rev. B 97, 144406 (2018)]. Theoretically, the first-principles calculations reveal the large interchain coupling, which leads to classical antiferromagnetic ordering and spin-flop-like transition. With this large interchain coupling, the exact diagonalization analysis yields 1/2 and 3/4 plateaus, showing the quantum origin of magnetization plateaus. Thus, ${\mathrm{Co}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ is an interchain-coupled system showing both classical and quantum behaviors.

In low-dimensional Ising spin systems, an interesting observation is the presence of step magnetization at low temperatures. Here we combine both DC and pulsed magnetic fields to study the 1/3 magnetization plateau and multiple steps in the Ising spin-chain material α-CoV2O6. Magnetization in pulsed fields is quite different from that in DC fields, showing multiple steps in an intermediate range of 4.2-6 K, inverted hysteresis below 4.2 K and asymmetric magnetization in negative fields below 11 K. We demonstrate that these unusual behaviors in magnetization are caused by the spin dynamics and the anomalous magnetocaloric effect (MCE) in α-CoV2O6, i.e., abrupt changes of sample temperature in adiabatic conditions. We successfully separate the influence between the intrinsic slow spin dynamics and the quasi-extrinsic temperature change. From the MCE, we find that some irreversible behavior is originated from the slow spin dynamics. Two different slow dynamics associated with the metastable steps are observed: one is sensitive to the slow field sweep rate at the order of ∼mT s-1and weakly depends on temperature, while the other responds to the rapid field sweep rate of ∼kT s-1and dominates at lowest temperature. We also distinguish that the metastable transition atH4is the first order and crucial for the ferrimagnetic to ferromagnetic transition. This study is useful to the understanding of multistep magnetization in α-CoV2O6and sheds light on recent experimental findings of related compounds.

Magnetization and high-field ESR measurements have been performed to study the magnetism of nanocrystals of α -CoV 2 O 6 , an Ising spin-chain system without triangular lattice but presenting interesting 1/3 magnetization step. The results demonstrated the antiferromagnetic (AFM) enhancement and gradual suppression of the 1/3 magnetization step in nanoparticle samples. Within the framework of core–shell model consisting of the AFM core spins and the uncompensated/disordered shell spins, the AFM enhancement below T N =13 K is a result of enhanced shell disorder with weak ferromagnetism. This AFM enhancement, along with the suppression of saturation magnetization, results in the suppression of 1/3 magnetization step. Furthermore, the paramagnetism of the shell was confirmed by our high-field ESR measurements. The time-dependent magnetization suggests the presence of spin-glass-like freezing. This is expected for nanoparticles with surface shell disorder with ferromagnetic correlations, but is not expected for bulk material of α -CoV 2 O 6 without spin frustration. These findings demonstrate that size tuning is an effective parameter for controlling the ground state of α -CoV 2 O 6 .

At the beginning of the 21st century, China began to transform and upgrade the old urban industrial areas. At present, it is relatively lack to research the post-evaluation system of functional upgrading and transformation for old urban industrial areas. This paper chooses and analyzes 24 typical projects of regeneration and transformation for old urban industrial areas through literature research. On the basis of analyzing the relevant literature research, policy implementation and practice results of typical projects, this paper proposes a post-evaluation system with comprehensive influence as the target and 5 influence dimensions and 21 evaluation factors through combining qualitative and quantitative techniques. Based on this, the connotation of evaluation factors is analyzed, so as to form a practical post-evaluation system of comprehensive influence.

A quantized magnetization plateau is usually not expected when a classic spin-flop transition occurs in a low-dimensional antiferromagnet. Here, we report an experimental observation of a spin-flop transition followed by a wide half-magnetization plateau in the $S=1$ skew-chain system ${\mathrm{Ni}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$. This plateau, which is stabilized in fields of 8--30 T, is realized through an exotic nematiclike phase transition for magnetic fields applied along all three crystallographic axes, resulting in rich anisotropic phase diagrams. We discuss a possible mechanism whereby the magnetic frustration and interchain interactions may cause this half-magnetization plateau, which is in agreement with our exact diagonalization result.

We report size reduction-induced chain breaking in the spin-1 Haldane-chain SrNi

Isolation of high-quality RNA free of contaminants, such as polyphenols, proteins, plant secondary metabolites, and genomic DNA from plant tissues, is usually a challenging but crucial step for molecular analysis. We developed a novel protocol based on the cetyltrimethylammonium bromide method to isolate high-quality RNA from blackberry plant tissues, especially fruits. Most DNA was removed when acetic acid was utilized, before RNA precipitation. Thus, lithium chloride, a reagent widely used for RNA purification, was not needed. The isolation time was shortened to less than 3 h. The RNA was quite pure, with little DNA contamination. The quality of the RNA was assessed by spectrophotometric readings and electrophoresis on agarose gels. It was good enough for downstream enzymatic reactions, such as reverse transcription-PCR, cloning and real-time PCR assay.

The nature of 4f-3d magnetic interaction in oxides as well as its influence on the magnetocaloric effect (MCE) is an interesting topic. Here, we report the weak magnetic interaction and large MCE in a new triangular lattice GdFeTeO6 synthesized by the solid state reaction method. The weak exchange, which was seldom observed in 4f-3d oxides, is supported by the low ordering temperature (TC ≤ 3 K) and a positive but small Curie-Weiss temperature (θp = 3 K). Under an external magnetic field, the magnetization process yields a large magnetic entropy change of 38.5 J kg−1 K−1 at 5 K for 0-7 T and 23.6 J kg−1 K−1 at 3 K for 0-3 T. Finally, our first-principles calculations demonstrate a ferrimagnetic spin model with the Gd(↑)-Gd(↑)-Fe(↓)-Fe(↓) configuration. The weak magnetic interaction is an average effect of ferromagnetic (4f-4f and 3d-3d) and antiferromagnetic (4f-3d) interactions. The antiferromagnetic 4f-3d interaction is a reason for the reduction of MCE.The nature of 4f-3d magnetic interaction in oxides as well as its influence on the magnetocaloric effect (MCE) is an interesting topic. Here, we report the weak magnetic interaction and large MCE in a new triangular lattice GdFeTeO6 synthesized by the solid state reaction method. The weak exchange, which was seldom observed in 4f-3d oxides, is supported by the low ordering temperature (TC ≤ 3 K) and a positive but small Curie-Weiss temperature (θp = 3 K). Under an external magnetic field, the magnetization process yields a large magnetic entropy change of 38.5 J kg−1 K−1 at 5 K for 0-7 T and 23.6 J kg−1 K−1 at 3 K for 0-3 T. Finally, our first-principles calculations demonstrate a ferrimagnetic spin model with the Gd(↑)-Gd(↑)-Fe(↓)-Fe(↓) configuration. The weak magnetic interaction is an average effect of ferromagnetic (4f-4f and 3d-3d) and antiferromagnetic (4f-3d) interactions. The antiferromagnetic 4f-3d interaction is a reason for the reduction of MCE.

Seven freak wave incidents previously documented in the real ocean in combination with model hindcast simulations are used to study the variations associated with freak wave-related parameters, such as wave steepness, directional spreading, and frequency bandwidth. Unlike the strong correlations between the freak wave parameters and freak waves' occurrence which were obtained in experimental and physical research, the correlations are not clear in the freak waves occurred in the real ocean. Wave directional spreading-steepness joint distribution is introduced and common visual features were found in the joint distribution when freak waves occur among seven "freakish" sea states. The visual features show that freak wave incidents occur when the steepness is large and directional spreading is small. Besides the steepness is large and directional spreading is small, a long-duration relatively rough sea state is also necessary for the freak wave generation. The joint distribution is more informative than the sequential variation of any single statistical wave parameter. The continuous sea states of local large steepness and small directional spreading are supposed to be "freakish" sea states, and two-dimensional distribution visualization is found to be a useful tool for freak waves forecast. The common visual features of joint distributions supply an important cue for the theoretical and experimental research.

In this note, we show that, in the one-dimensional case, as an approximation to residual-free bubbles (RFB), certain practical bubbles can be applied to obtain a scheme which is uniformly convergent with respect to small viscosity in the energy norm for advection-diffusion problems.

Isolation of high-quality RNA free of contaminants, such as polyphenols, proteins, plant secondary metabolites, and genomic DNA from plant tissues, is usually a challenging but crucial step for molecular analysis. We developed a novel protocol based on the cetyltrimethylammonium bromide method to isolate high-quality RNA from blackberry plant tissues, especially fruits. Most DNA was removed when acetic acid was utilized, before RNA precipitation. Thus, lithium chloride, a reagent widely used for RNA purification, was not needed. The isolation time was shortened to less than 3 h. The RNA was quite pure, with little DNA contamination. The quality of the RNA was assessed by spectrophotometric readings and electrophoresis on agarose gels. It was good enough for downstream enzymatic reactions, such as reverse transcription-PCR, cloning and real-time PCR assay. The method yielded an amount of total RNA comparable to previously described protocols.