Linear Chain System Research Articles

Efficiency of electron transport processes

Abstract Efficiency of electron transport along the linear chain of molecules was investigated from a dynamic viewpoint. It was proposed that two kinds of efficiency are important for electron transport; one is energy efficiency, the other quantum efficiency. In this paper, these two efficiencies are defined for a linear chain system and the correlation between these quantities and the arrangement of various electron transfers is investigated. The optimization of energy and quantum efficiency is found to set different conditions on the arrangement of the rate constants of electron transfer, and there is strong correlation between neighboring electron transfers. In order to maximize both efficiencies, the rate constants of forward and backward transfers of electrons should be bounded by one another in a limited range. In particular, when there are some bypass reactions on the linear chain, as is the case for photosynthesis and respiration, the rate of the backward transfer should be the same order of magnitude as that of the next forward transfer. The present results are applied to some biological processes. In the early stage of photosynthetic electron transfer it seems that quantum efficiency is more important than energy efficiency. The quantum efficiency is close to unity, whereas a considerable part of the free energy is wasted as heat during the primary electron transfers. On the other hand, in the slower electron transfer processes in photosynthesis and respiration, which take place mostly near equilibrium, the energy efficiency seems to be more important than the quantum efficiency. The relation of these properties to biological function is discussed.

ESR Study of Mn2+in the Impure Ising Linear Chain [(CH3)3NH]CoCl3·2H2O: Mn

ESR investigation was carried out on the impure Ising linear-chain compound [(CH 3 ) 4 NH]CoCl 3 ·2H 2 O: Mn in the temperature range 1.8–300 K at 24 GHz. Only single lines with g =2 for Mn 2+ are observed within the temperature range 10–80 K. Below about 10 K five lines corresponding to the fine structure of Mn 2+ and two spin-cluster resonances for the Co 2+ linear-chain system appear for orientations H // c and H // b , respectively. The anisotropy of the fine structure spectrum can be explained only by recognizing the canceling in the diagonal part of the Mn–Co interaction tensor.

Low-dimensionality magnetic interactions in the linear-chain transition metal complexes M(2,2′-bipyridine)(H 2O) 2SO 4 ( M = Fe, Ni, and Cu)

The magnetic susceptibilities of polycrystalline samples of the chain compounds M(2,2′-bipyridine)(H 2O) 2SO 4 ( M = Fe, Ni, and Cu) have been measured in the temperature range 1.7 to 300 K. The iron and nickel compounds exhibit broad maxima in χ′ M vs T at ∼ 8 K. The experimental results can be interpreted in terms of antiferromagnetic linear-chain systems and provide information on the magnitude of the intrachain interactions. Zero-field Mössbauer spectra of a powder sample of trans-μ-sulfato-diaquo(2,2′-bipyridine)iron(II) over the preceding range were also determined. The chemical isomer shift value corresponds to 6-coordinate high-spin iron(II). Below 2.0 K the compound exhibits magnetic hyperfine splitting, suggesting long-range, three-dimensional ordering with a critical temperature of T N ≲ 1.7 K. By means of Oguchi's Green's function theory and the experimentally determined transition temperature T N, an estimate of the ratio of the inter- to intrachain exchange interaction is obtained.

Magnetic behavior of the ferromagnetic quantum chain systems (C6H11NH3)CuCl3(CHAC) and (C6H11NH3)CuBr3(CHAB)

Heat-capacity measurements on (C6H11NH3)CuBr3 (CHAB) in the region 0.45 < T<55 K are presented. Three-dimensional ordering is observed at Tc=1.50 K. The data are analyzed together with previously reported measurements on (C6H11NH3)CuCl3 (CHAC). Both compounds appear to be very good approximations of a ferromagnetic S=12 Heisenberg linearchain system with Jk50 K. From the data it is inferred that the intrachain interaction of CHAC contains about 2% uniaxial anisotropy, whereas CHAB contains about 5% easy-plane anisotropy. The results are corroborated by magnetization measurements on CHAB below Tc, which also reveal a metamagnetic transition for Hb (Hc=210Oe). From the value of Hc and the location of the tricitical point the interchain interactions in CHAB were found as zAFJAFk=-0.03 K, zFJFk0.08 K.

AFMR study of CuCl2⋅DMSO: A pseudo-one-dimensional system with ferromagnetic intrachain interactions

CuCl2⋅DMSO is a linear chain system with strong ferromagnetic intrachain coupling (J/k = 45 K) and significant interchain coupling (J′/k = −1.6 K). It orders three-dimensionally near 5 K and undergoes a spin-flop transition at low fields (3–4 kOe). The AFMR modes have been observed in the temperature range 1.5–5.5 K. In addition, the spin-flop transition has also been observed due to the cut-off of the AFMR signal at the transition field. The easy and hard axes lie in the ac plane of the monoclinic crystal, with the easy axis making an angle of 55° with the chain direction. Interpretation of the data indicates that the system has nearly XY anisotropy, with a rhombic component approximately 5% of the XY anisotropy. It is observed that the spin-flop field increases as the temperature is lowered, from 3200 G at 5.4 K to 4100 kG at 2 K.

Pressure induced phase transition in the highly anisotropic compound: Y2[Pt(CN)4]3·21H2O

Abstract For the linear chain system Y2[Pt(CN)4]3·21H2O a pressure induced phase transition is observed by emission spectroscopy. At ptrans=(5±0.5) kbar and T=295 K the compound undergoes a first order phase transition, in the course of which the intra-chain Pt-Pt distance R shrinks by ΔR≈ -0.03 A . An approximate value had already been found at standard pressure for a temperature induced phase transition (Ttrans=218 K).

A new method for calculation of the magnetic properties in one- and two-dimensional spin systems with anisotropic Heisenberg exchange

A new approximation method is proposed for the calculation of the magnetic susceptibility of one-dimensional assembly of spins and the critical temperature of two-dimensional one both with the anisotropic Heisenberg exchange. In a linear chain system, every spins are grouped into pairs of adjacent spins (pair-approximation) or clusters of adjacent three spins (( q+1)-approximation), and the partition function of the total spin system is approximated as a sum of products of the partitions functions for the pairs or the clusters. Then the partition function of the anisotropic Heisenberg spin system is shown to reduce into a form of the Ising spin system with modified coupling constants. The exact result for the Ising chain system enables us to obtain an analytical expression for the magnetic susceptibility of anisotropic Heisenberg chain system. The same approximations are also applied to two-dimensional lattices, and the critical temperatures of the square, triangular, and honeycomb lattices with anisotropic Heisenberg exchange are calculated as a function of anisotropy parameter. The results are compared with those of the existing theories and shown to be quite excellent.

Observations of Short-Range Order by Optical Birefringence in One-Dimensional Antiferromagnets CsNiCl3, RbNiCl3and CsCoCl3

Magnetic short-range order was observed in one-dimensional S =1 Heisenberg (CsNiCl 3 , RbNiCl 3 ) and \(S{=}\frac{1}{2}\) Ising antiferromagnet (CsCoCl 3 ) up to k T ∼10| J | and 3| J |, respectively, by measuring optical birefringences. An isomorphic diamagnet CsMgCl 3 was used, with corresponding states argument, to extract the magnetic contribution Δ n m from the resultant birefringence Δ n in these magnetic systems. The temperature T max , at which the temperature derivative of the magnetic part Δ n m displays a broad maximutm, is in agreement with that predicted by the rigorous theory for the specific heat in each linear chain system.

Soliton lattice stability in a coupled linear chain system

We have demonstrated that in the weak coupling limit the soliton lattice of a coupled linear chain system is stable at low temperatures. All the harmonics of the soliton lattice exhibit the three-dimensional crossover at the same temperature which is also equal to the crossover temperature of the average discommensuration shift, the only to remain in absence of the commensurability potential.

Double ordering in magnetic linear chain systems

CsNiCl 3 and CsNiBr 3 each display two magnetic phase transitions at low temperatures. The existence of a specific heat spike at each transition in these salts, together with cesium NMR data, require that the higher temperature phase be ordered in the c-axis spin components but paramagnetic in the remaining spin component̃s. A reexamination of CsNiCl 3 shows the cesium NMR data to be consistent with the spin structures in both ordered phases.

Magnetic properties of linear chain systems: Metamagnetism of single crystal Co(pyridine)2Cl2

The metamagnetic behavior of the low temperature properties of single crystal Co(pyridine)2Cl2 is discussed. At 1.25 K oriented single crystals exhibit a two-step metamagnetic transition at applied fields ∼0.8 and 1.6 kG along the b-axis, a single transition at ∼0.7 kG for applied fields along the a* axis, and a single transition at ∼4.2 kG for an applied field along the c axis. Just above the transition fields a moment of 2μB/Co atom is measured for B0 parallel to the a* axis or b axis, and 0.4μB/Co atom is measured for the B0 parallel to the c axis. A large field dependent moment is observed at high fields. Many features of this compound closely mirror the behavior of CoCl2⋅2H2O. However, the Co(pyridine)2Cl2 has a much smaller interchain exchange, so that many features can be examined at lower fields. The basic features are consistent with a six-sublattice model for the ordered antiferromagnetic system. Measurements of magnetic moment versus temperature show that Co(pyridine)2Cl2 does not obey a Curie–Weiss law even at relatively high temperatures.

Proton spin-lattice relaxation experiments on S= Heisenberg antiferromagnetic linear chains

Abstract The dynamical behaviour of the S = 1 2 Heisenberg antiferromagnetic linear-chain system in single crystals CuSeO 4 .5H 2 O is investigated through proton spin-lattice relaxation experiments. This insulator contains besides the linear-chain system with exchange interaction J/k =-0.85 K, a paramagnetic system with θ=0.05 K. The dynamic properties of both magnetic systems have been studied extensively as a function of field (5–15 kOe) and temperature (0.3–20 K) and prove to be quite different. The contributions of these two systems to the relaxation of different protons are separated. The use of single crystals allows a study of T 1 as a function of the direction of the external field. Moreover the large dipolar fields at the proton sites due to the presence of the paramagnetic system, provide the unique opportunity for a chain system to study the relaxation times of different singular resonance lines. The spin-lattice relaxation of protons that interact dominantly with the paramagnetic system is governed by the spectral density of the auto-correlation function of the z component of the paramagnetic electron spins. The relaxation of protons close to the ALC system, however, proves to be governed by the spectral densities of the auto-correlation function of both the parallel and perpendicular component of the nearest ALC electron spin, φ z 0 (ω n ) and φ + 0 (ω n ). A study of the angular dependence of T 1 shows that these spectral densities of the ALC system exhibit different field and temperature dependencies. Particularly the difference in the temperature dependence is striking: φ z 0 (ω n ) decreases towards lower temperatures, whereas φ + 0 (ω n ) is temperature independent.

Non-linear modes in the condensed peierls phase

The equations of motion for the order parameters of a coupled linear chain system in a condensed Peierls phase are derived from a microscopic Hamiltonian. These results now provide the correct non-linear terms which are needed to discuss solitary wave excitation modes. The computation reported here is a mean field result, at T = 0, and with interchain electron backscattering. Amplitude solitary waves are energetically disallowed, but phase solitons (φ-particles) with small associated amplitude variation are possible.

Study of Magnetic Energy in One-Dimensional S=1/2 Heisenberg Antiferromagnet KCuF3 by Optical Birefringence

Measurements of optical birefringence have been made on single crystals of the a-type KCuF 3 between 6 and 600 K. The observed temperature dependence of birefringence was found to be in good agreement over a wider temperature range above T N with Bonner-Fisher's theoretical results for the magnetic energy of S =1/2 Heisenberg linear chain systems.

An exact dynamical solution to a linear chain doublet exciton with exponential memory

An exact analytic solution to the non-Markoffian spin one-half exciton linear chain system is found by diagonalising and Laplace transforming the coupled space and spin equations. As a particular example, numerical calculations of the time evolution of the two-site exciton system are presented for several realistic values of space and spin memory times. The unimportance of the cross-channel non-Markoffian behaviour for the cases where the space and spin memory times differ by at least a factor of ten is illustrated by comparison with the traditional Pauli master equation solutions. The memory can lead to oscillating populations which, on time scales shorter than or comparable with the relevant memory time, look like coherent transfer. Coherent motion can be observed, for certain values of the parameters, in the slower channel long after the more normal channel has become Markoffian. Interference regimes are possible, but require similar values of space and spin transfer integrals; this is improbable for organics.

Quasi-one-dimensional behavior of(CH3)2NH2MnCl3(DMMC)

The heat capacity of dimethyl ammonium manganese trichloride has been investigated for $1.6&lt;T&lt;50$ K. A transition to a three-dimensional antiferromagnetically ordered state has been observed at 3.60 K, which is supported by nuclear-magnetic-resonance and susceptibility measurements. The critical entropy did amount to 3.4%. The magnetic heat capacity in the paramagnetic region could be described very well by a $S=\frac{5}{2}$ Heisenberg linear chain system with $\frac{J}{k}=\ensuremath{-}5.8\ifmmode\pm\else\textpm\fi{}0.7$ K. The data for $\frac{\mathrm{kT}}{|J|}&lt;1.5$, together with the earlier data on ${(\mathrm{C}{\mathrm{H}}_{3})}_{4}$NMn${\mathrm{Cl}}_{3}$, corroborate the suggested low-temperature behavior of such a system.

Effects of randomness on three-dimensional magnetic ordering of quasi-low-dimensional spin systems

Motivated by recent work of Hone and co-workers on three-dimensional (3D) ordering of impure Ising and classical Heisenberg linear-chain systems, we present a coherent-potential-approximation (CPA) analysis of quasi-one-dimensional and nearly-two-dimensional spin systems with Heisenberg exchange coupling for which 3D magnetic ordering, in the absence of spatial randomness, is assumed to be described by a random-phase decoupled Green's-function theory. The effects caused by the introduction of arbitrary concentration of nonmagnetic impurities, with quenched-in random distribution and with or without the simultaneous presence of exchange-bond randomness between magnetic ions, are analyzed within such a CPA procedure. Numerical results for the renormalization of spin-wave stiffness along various symmetry directions and for the 3D transition temperature are given as a function of the (arbitrary) impurity concentration. Qualitative comparison with the results given by Hone et al. can be carried out and it is found that in the regime of very small interchain coupling strengths and impurity concentrations, where the latter theory can be expected to be reliable, these results are in reasonable agreement with theirs. Similarly, in the large-impurity limit near the percolation threshold, we find the behavior of the present results to be in accord with that generally expected for such systems. Lastly, we note that our procedure indicates that spatial isotropy of the spin-wave dispersion is "effectively" achieved at some intermediate concentration, the magnitude of which depends on the relative size \ensuremath{\alpha} of the inter- and intrachain couplings.

ChemInform Abstract: PHYSICAL PROPERTIES OF LINEAR‐CHAIN SYSTEMS. 7. MAGNON SIDEBANDS IN THE ELECTRONIC ABSORPTION SPECTRA OF CESIUM TRICHLOROCOBALTATE AND RUBIDIUM TRICHLOROCOBALTATE

Chemischer InformationsdienstVolume 8, Issue 30 Physical Inorganic Chemistry ChemInform Abstract: PHYSICAL PROPERTIES OF LINEAR-CHAIN SYSTEMS. 7. MAGNON SIDEBANDS IN THE ELECTRONIC ABSORPTION SPECTRA OF CESIUM TRICHLOROCOBALTATE AND RUBIDIUM TRICHLOROCOBALTATE C. F. PUTNIK, C. F. PUTNIKSearch for more papers by this authorS. L. HOLT, S. L. HOLTSearch for more papers by this author C. F. PUTNIK, C. F. PUTNIKSearch for more papers by this authorS. L. HOLT, S. L. HOLTSearch for more papers by this author First published: July 26, 1977 https://doi.org/10.1002/chin.197730013AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume8, Issue30July 26, 1977 RelatedInformation

Anomalous electrical properties of linear chain mercury compounds

The electrical resistivity of Hg 2.86AsF 6 has been studied as a function of temperature. At room temperature, the resistivity along the chain direction is 10 −4 Ω-cm with an anisotropy of about 10 2. This incommensurate linear chain system remains metallic at low temperatures with resistance ratio ϱ ab(300 K)/ ϱ ab(1.4 K) ≅ 3000 and still increasing with no apparent sign of residual resistivity. A large anisotropic magnetic field dependence of the resistivity is observed below 30 K. Near 4 K, the c-axis resistance drops abruptly more than three orders of magnitude, apparently to zero, while ϱ ab is continuous. The c-axis transition is suppressed in a small magnetic field.

Solitons in a Coupled Linear Chain System

Solitons in a Coupled Linear Chain System