Antiferromagnetic Chain System Research Articles

Surface <i>Free Energy</i> of <i>Photon echo on</i> DNA Molecules: Theoretical Study

We have study here the topological properties as w ell as the elastic and thermodynamical properties of DNA molecules from an analysis of an antiferromagnetic spin chain system. The topological property such as the linking number can be derived from the Chem-Simons topology associated with a quantum spin and two indistinguishable fermions are made relatively diverse earlier entanglement, through giving one qubit spin to one of them done the circularly split attractive field that plays the character of shifting the path of quantization axis. Therefore the reverberation arise and the spin must development the transformation of entangled state from symmetric to antisymmetric state finished the closed path. This spin of the attractive field efficiently corresponds near the variation in the path of the flux line. It is exposed that the entanglement of two DNA molecule place spin-echo to one of them marks the transform of Berry phase that can be exact as a analyse of entanglement photon echo technique. If we apply this technique to one spinor previously entanglement by other then the Berry phase is surrounded in the entangled state, consequential the exclusion of dynamical time. This is found to be in good agreement with the thermodynamic entropy as entanglement entropy, charge of encircle a inelastic polymer string bounded by a fine tube.

Wide Magnetic Thermal Memory Effect (∼55 K) Above Room Temperature Coupled to a Structure Phase Transition of Lattice Symmetry Reduction in High-Temperature Phase in an S = 1/2 Spin Chain Molecule Crystal.

One-dimensional (1D) S = 1/2 Heisenberg antiferromagnetic (AFM) chain system shows frequently a spin-Peierls-type transition owing to strong spin-lattice coupling. From high-temperature phase (HTP) to low-temperature phase (LTP), the spin chain distortion leads to the reduction in lattice symmetry in LTP, called the symmetry breaking (SB) phase transition. Herein, we report the first example of 1D S = 1/2 AFM molecular crystal, [Et3( n-Pr)N][Ni(dmit)2] (Et3( n-Pr)N+ = triethylpropylammonium, dmit2- = 2-thioxo-1,3-dithiole-4,5-dithiolate), which shows a structural phase transition with lattice symmetry increase in LTP, which is contrary to the SB phase transition. Particularly, the structure phase transition leads to magnetically bistable state with TC↑ ≈ 375 K, TC↓ ≈ 320 K, and surprisingly large thermal hysteresis (∼55 K). Additionally, LTP and HTP coexist in a temperature region near TC but not at TC in this 1D spin system. The large hysteresis is related to the huge deformation of anion stack, which needs high activation energy for the structure transformation and magnetic transition between LTP and HTP. This study would not only provide new insight into the relationship of spin-Peierls-type transition and structure phase transition but also offer a roadmap for searching molecular-scale magnetic bistable materials, which are in huge demand in future electronic, magnetic, and photonic technologies.

Quantum Criticality of an Ising-like Spin-1/2 Antiferromagnetic Chain in a Transverse Magnetic Field.

We report on magnetization, sound-velocity, and magnetocaloric-effect measurements of the Ising-like spin-1/2 antiferromagnetic chain system BaCo_{2}V_{2}O_{8} as a function of temperature down to 1.3K and an applied transverse magnetic field up to 60T. While across the Néel temperature of T_{N}∼5 K anomalies in magnetization and sound velocity confirm the antiferromagnetic ordering transition, at the lowest temperature the field-dependent measurements reveal a sharp softening of sound velocity v(B) and a clear minimum of temperature T(B) at B_{⊥}^{c,3D}=21.4 T, indicating the suppression of the antiferromagnetic order. At higher fields, the T(B) curve shows a broad minimum at B_{⊥}^{c}=40 T, accompanied by a broad minimum in the sound velocity and a saturationlike magnetization. These features signal a quantum phase transition, which is further characterized by the divergent behavior of the Grüneisen parameter Γ_{B}∝(B-B_{⊥}^{c})^{-1}. By contrast, around the critical field, the Grüneisen parameter converges as temperature decreases, pointing to a quantum critical point of the one-dimensional transverse-field Ising model.

Comparison of the Vibrational Spectra of Copper Polysilicate, CuSiO<sub>3</sub>, with Those of the Prototypic Copper Polygermanate, CuGeO<sub>3</sub>

Orthorhombic copper polysilicate, CuSiO3, is isotypic to the spin-Peierls compound CuGeO3 and represents a further example of a quasi-one-dimensional spin = 1/2 antiferromagnetic Heisenberg chain system. This is a representation of the first Raman and IR/FIR spectra for CuSiO3, measured at room temperature on polycrystalline samples. A comparison of the optical phonons, predicted by a factor group analysis, with those observed for the CuGeO3 prototype, is presented. A mode assignment for the silicate is given. Surface effects due to a very small crystallite size may cause additional broad bands observed in the Raman spectrum of CuSiO3. From the analysis of the Davydov doublet an intralayer-to-interlayer bond strength of about 40 is derived for the silicate, which is about 20% lower than for the isotypic germanate, allowing for different magnetic responses at low temperature.

Magnetic ordering in the ultrapure site-diluted spin chain materialsSrCu1−xNixO2

Muon spin rotation technique is used to study magnetic ordering in ultra-pure samples of SrCu$_{1-x}$Ni$_x$O$_2$, an archetypical $S=1/2$ antiferromagnetic Heisenberg chain system with a small amount of $S=1$ defects. The ordered state in the parent compound is shown to be highly homogeneous, contrary to previous report [M. Matsuda et al., Phys. Rev. B \textbf{55}, R11953 (1997)]. Even minute amount of Ni impurities result in inhomogeneous order and a decrease of the transition temperature. At as little as $0.5$~\% Ni concentration, magnetic ordering is entirely suppressed. The results are compared to previous theoretical studies of weakly coupled spin chains with site-defects.

A study of the magnetic properties of a quasi-one-dimensional magnet β-TeVO4 in the frame of the J1–J2 model

Magnetic properties of single crystal β-TeVO4 with a zigzag chain of magnetic centers (V4+ ions, S = 1/2) are analyzed in the framework of the J1–J2 model. The best agreement with experimental data is obtained for the J1–J2 model with parameters J1/kB = −38.33 K and J2/kB = 29.48 K (gb = 2.07, ga,c = 1.99). In contrast to the previously used model (a uniform antiferromagnetic spin chain system with J1/kB = 21.4 K (gb = 2.28, ga,c = 2.18)), this improved result allows one to consider the object under study as a zigzag chain system with a dominant ferromagnetic exchange between the nearest neighbors and an antiferromagnetic interaction between the next-nearest neighbors.

Ba2Cu2Te2P2O13: A new telluro-phosphate with S=1/2 Heisenberg chain

A new telluro-phosphate compound Ba2Cu2Te2P2O13 with S=1/2 Heisenberg chain has been successfully synthesized by solid state reaction and grown by flux method. Single crystal X-ray diffraction reveals that Ba2Cu2Te2P2O13 crystallizes into a monoclinic space group C2/c and cell parameters of a=17.647(3)Å, b=7.255(2)Å, c=9.191(2)Å and β=100.16 (3)°. In the structure of Ba2Cu2Te2P2O13, one dimensional [CuTePO7]3− chains are formed by tetrahedral PO4 and trigonal bi-pyramidal TeO4 joining square planar CuO4 groups. Those [CuTePO7]3− chains are inter-connected by sharing one oxygen atom from the TeO4 group to form two dimensional layers. Magnetic susceptibility and specific heat measurements confirm that the title compound is a model one dimensional Heisenberg antiferromagnetic chain system.

ESR of coupled spin-1/2 chains in copper pyrazine dinitrate: unveiling geometrical frustration

The spin dynamics of copper pyrazine dinitrate (Cu(C4H4N2)(NO3)2), a model spin-1/2 Heisenberg antiferromagnetic (AF) chain system, was investigated by means of electron spin resonance (ESR). Using the high-field ESR we evidenced the inequivalence of Cu sites belonging to adjacent spin chains in the ac planes of this compound. It was revealed that the dominating interchain interaction is of zig-zag-type. This interaction gives rise to geometrical frustration strongly affecting the character of AF ordering. Combining our experimental findings with the results of a quasiclassical approach we predict that at low temperatures the system orders in an incommensurate spiral state.

Magnetic phase diagrams, domain switching, and quantum phase transition of the quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8

In the effective Ising spin-1/2 antiferromagnetic chain system BaCo${}_{\text{2}}$V${}_{\text{2}}$O${}_{\text{8}}$ the magnetic-field influence is highly anisotropic. For magnetic fields along the easy axis $c$, the N\'eel order is strongly suppressed already at low fields and an incommensurate order is entered above 4 T. We present a detailed study of the magnetic phase diagrams for different magnetic field directions, which are derived from magnetization data, high-resolution thermal expansion, and magnetostriction measurements as well as from the thermal conductivity. Zero-field thermal-expansion data reveal that the magnetic transition is accompanied by an orthorhombic distortion within the $ab$ plane. Under ambient conditions the crystals are heavily twinned, but the domain orientation can be influenced either by applying uniaxial pressure or a magnetic field along the [100] direction. In addition, our data reveal a pronounced in-plane magnetic anisotropy for fields applied within the $ab$ plane. For $H\phantom{\rule{0.16em}{0ex}}\ensuremath{\parallel}\phantom{\rule{0.16em}{0ex}}[110]$, the magnetic field influence on ${T}_{\text{N}}$ is weak, whereas for magnetic fields applied along [100], ${T}_{\text{N}}$ vanishes at about 10 T and the zero-field N\'eel order is completely suppressed as is confirmed by neutron diffraction data. The second-order phase transition strongly suggests a quantum critical point being present at $H\ensuremath{\simeq}10$ T parallel [100].

Magnetic phase diagram of the frustratedS=12chain magnet LiCu2O2

We present the results of the magnetization and dielectric constant measurements on untwinned single-crystal samples of the frustrated $S=1/2$ chain cuprate LiCu${}_{2}$O${}_{2}$. Magnetic phase transitions were observed. A spin-flop transition of the spiral spin plane was observed for the field orientations $\mathbit{H}\ensuremath{\parallel}\mathbit{a}$, $\mathbit{b}$. The second magnetic transition was observed at $H\ensuremath{\approx}15$ T for all three principal field directions. This high-field magnetic phase is discussed as a collinear spin-modulated phase, which is expected for an $S=1/2$ nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic chain system.

ChemInform Abstract: Description of Anhydrous (Black) Dioptase as a S = 1/2 Uniform Antiferromagnetic Chain System.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Description of Anhydrous (Black) Dioptase as a S = 1/2 Uniform Antiferromagnetic Chain System

AbstractThe structural and magnetic properties of anhydrous (black) dioptase, CuSiO3, were investigated by carrying out single‐crystal X‐ray diffraction, specific heat, and magnetic susceptibility measurements as well as by performing spin dimer analysis based on extended Hückel tight‐binding calculations. Our spin dimer analysis indicates that black dioptase is a S = 1/2 uniform antiferromagnetic chain system with the interchain spin exchange weaker than the intrachain exchange by three orders of magnitude. Specific heat and magnetic susceptibility measurements show that the intrachain exchange is –174(2) K, and the interchain exchange is of the order of ~2 K. They lead to long‐range magnetic ordering at about 5 K as evidenced by a broad anomaly in the specific heat.

Synthesis and structural characterization of2Dioxane⋅2H2O⋅CuCl2: Metal-organic compound with Heisenberg antiferromagneticS=12chains

A novel organometallic compound 2Dioxane.CuCl2.2H2O has been synthesized and structurally characterized by X-ray crystallography. Magnetic susceptibility and zero-field inelastic neutron scattering have also been used to study its magnetic properties. It turns out that this material is a weakly coupled one-dimensional S=1/2 Heisenberg antiferromagnetic chain system with chain direction along the crystallographic c axis and the nearest-neighbor intra-chain exchange constant J=0.85(4) meV. The next-nearest-neighbor inter-chain exchange constant J' is also estimated to be 0.05 meV. The observed magnetic excitation spectrum from inelastic neutron scattering is in excellent agreement with numerical calculations based on the Muller ansatz.

Quantum critical dynamics of anS=12antiferromagnetic Heisenberg chain studied byC13NMR spectroscopy

We present a $^{13}\text{C}$ NMR study of the magnetic field driven transition to complete polarization of the $S=\frac{1}{2}$ antiferromagnetic Heisenberg chain system copper pyrazine dinitrate $\text{Cu}({\text{C}}_{4}{\text{H}}_{4}{\text{N}}_{2}){({\text{NO}}_{3})}_{2}$ (CuPzN). The static local magnetization as well as the low-frequency spin dynamics, probed via the nuclear spin-lattice relaxation rate ${T}_{1}^{\ensuremath{-}1}$, were explored from the low to the high field limit and at temperatures from the quantum regime $({k}_{B}T⪡J)$ up to the classical regime $({k}_{B}T⪢J)$. The experimental data show very good agreement with quantum Monte Carlo calculations over the complete range of parameters investigated. Close to the critical field, as derived from static experiments, a pronounced maximum in ${T}_{1}^{\ensuremath{-}1}$ is found which we interpret as the finite-temperature manifestation of a diverging density of zero-energy magnetic excitations at the field-driven quantum critical point.

Integrable spin chains on the conformal moose: Script N = 1 superconformal gauge theories as six-dimensional string theories

We consider N=1, D=4 superconformal U(N)^{pq} Yang-Mills theories dual to AdS_5xS^5/Z_pxZ_q orbifolds. We construct the dilatation operator of this superconformal gauge theory at one-loop planar level. We demonstrate that a specific sector of this dilatation operator can be thought of as the transfer matrix for a two-dimensional statistical mechanical system, related to an integrable SU(3) anti-ferromagnetic spin chain system, which in turn is equivalent to a 2+1-dimensional string theory where the spatial slices are discretized on a triangular lattice. This is an extension of the SO(6) spin chain picture of N=4 super Yang-Mills theory. We comment on the integrability of this N=1 gauge theory and hence the corresponding three-dimensional statistical mechanical system, its connection to three-dimensional lattice gauge theories, extensions to six-dimensional string theories, AdS/CFT type dualities and finally their construction via orbifolds and brane-box models. In the process we discover a new class of almost-BPS BMN type operators with large engineering dimensions but controllably small anomalous corrections.

Specific Heat Study of Novel Spin-Gapped System: (CH3)2NH2CuCl3

Specific heat measurements in a magnetic field up to 8 T have been performed on an S =1/2 weakly coupled alternating ferromagnetic (F) and antiferromagnetic (AF) dimer chain system, (CH 3 ) 2 NH 2 CuCl 3 . We have observed a spontaneous AF ordering and a field-induced one below and above the 1/2 magnetization plateau field range from 2 to 3.5 T, respectively. The H – T phase boundaries for the orderings are completely different from the general reentrant ones of the other quantum spin systems investigated thus far. In the plateau field range, a double-peaked structure is observed in the temperature dependence of specific heat, reflecting the coexistence of F and AF excitations.

Polarized inelastic neutron scattering in the quasi-one-dimensional antiferromagnet KCuF 3

The material KCuF 3 is a prototypical example of a weakly coupled S=1/2 Heisenberg antiferromagnetic chain system. The inter-chain coupling leads to antiferromagnetic order at low temperatures. In the ordered state theory predicts that the low-energy spin dynamics exhibits an unusual gapped longitudinal mode. Here we report polarized inelastic scattering measurements of the excitations in KCuF 3. A weak magnetic field is utilized to prepare a single domain state with the spins aligned in the scattering plane but perpendicular to the chain direction. This configuration enables a clean measurement of the longitudinal magnetic response as spin-flip scattering.

ESR Experiments on Quantum Spin Systems

Our recent work is reviewed with focus on unique features of the application of Electron Spin Resonance (ESR) technique for quantum spin systems, together with a brief survey of historical backgrounds and recent progress in ESR and model systems. A example is presented in order to illustrate ESR powerfulness in view of high sensitivity, high energy resolution, and feasibility of high field measurements by using pulsed magnetic fields. We apply the ESR technique to observe directly, for the first time, quantum sine-Gordon excitations which have paramount importance in understanding unique quantum magnetism of the S =1/2 Heisenberg antiferromagnetic chain system, Cu-benzoate.

High Field ESR Study of BaCu2(Si1-xGex)2O7Single Crystal

Recent advance of a field theoretical approach of a low-temperature electron spin resonance (ESR) in S=½ antiferromagnetic chain, which has Dzyaloshinskii-Moriya (DM) interactions and staggered g-tensor sites, by Oshikawa and Affleck (OA) suggests peculiar magnetic field dependence of ESR. Although BaCu 2 (Si 1 - x Ge x ) 2 O 7 is an antiferromagnetic chain system with mixed antiferromagnetic and ferromagnetic interchain interactions, we found that x=0.65 substance shows the peculiar field dependence of ESR predicted by OA theory. The temperature dependence of the line width showed the power-law dependence and strong field dependence in the gapless spinon regime which can be well interpreted by OA theory. The temperature dependence of the resonance shift turned out to be also consistent with OA theory. These results are also discussed in connection with Cu-Benzoate which is considered as a model substance of OA theory.

Submillimeter wave ESR of S = 1 antiferromagnetic Heisenberg chain system with bond alternation

Submillimeter wave ESR of Ni 2(μ-C 2O 4)(μ-N 3)(Medpt) 2(ClO 4) has been performed. A broad resonance has been observed above 10 K at 300 GHz for H ⊥ chain. We also have measured frequency dependence of the resonance. The energy gap and the anisotropy term DS 2 z of this system is discussed from our results.