Tetramethylammonium Manganese Trichloride Research Articles

Combined Magnetic and Single-Crystal X-ray Structural Study of the Linear Chain Antiferromagnet [(CH3)4N][MnCl3] under Varying Pressure

The magnetic susceptibility and single-crystal X-ray structure of the one-dimensional Heisenberg antiferromagnetic chain tetramethylammonium manganese trichloride (TMMC) have been studied under pressure as a facile route to develop structure-property relationships. The X-ray structure of TMMC was determined at 0, 2.1, 3.8, 6.8, 12.2, and 17.0 kbar using diamond-anvil cell techniques and synchrotron radiation. The space group is confirmed to be P6(3)/m up to 17 kbar, and structural refinement shows that the Mn-Mn separations between and along the chains change by about 3.4 and 2.5%, respectively, over 17 kbar. A structural transition from hexagonal to monoclinic symmetry possibly occurs at 17 kbar, associated with a loss of crystal quality. Variable-temperature magnetic susceptibility data were taken at 0, 0.3, 1.5, 2.9, 4.0, 5.2, and 6.5 kbar and show that the intrachain coupling constant changes from -6.85 to -7.81 K over this range. The interchain coupling constant of -0.54 K can also be extracted from the Fisher model modified for interacting chains. The pressure-temperature diagram shows the slope of the intrachain antiferromagnetic coupling with pressure, DeltaT(IAF)/DeltaP, changes from 0.5 to 1.6 K/kbar at 2 kbar where the structure changes from P2(1)/a to P2(1)/m. Comparison of the magnetic and structural data are consistent with the power-law relationship developed by Bloch where J proportional, variant r-n, r = Mn...Mn separation and n approximately 10.

Diffusion-limited exciton fusion reaction in one-dimensional tetramethylammonium manganese trichloride (TMMC).

We present results of an experimental study on the reaction kinetics of a one-dimensional diffusion-reaction system, on a picosecond to millisecond time scale. Tetramethylammonium manganese trichloride (TMMC) is a perfect model system to study this problem. Time-resolved luminescence of TMMC has been measured over nine decades in time. The nonexponential shape of the luminescence decay curves depends strongly on exciting laser power. This is shown to result from a fusion reaction (A+A\ensuremath{\rightarrow}A) between photogenerated excitons, which is very well described by the diffusion-limited single-species fusion model for initial exciton densities 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ (fraction of the number of sites). At higher initial exciton densities the diffusion process, and thus the reaction rate, is significantly influenced by the heat produced in the fusion reaction. This is supported by Monte Carlo simulations.

Thermal conductivity of the ferromagnetic chain system CsNiF3.

The thermal conductivity \ensuremath{\lambda} of ${\mathrm{CsNiF}}_{3}$ has been measured in the region 2.5 KT10 K with the heat flow parallel to the chain direction. Fields up to 8 T were applied both within and perpendicular to the easy plane. The data on this ferromagnetic chain system indicate that the effect of solitons on \ensuremath{\lambda} is very small, in agreement with earlier observations on [${\mathrm{C}}_{6}$${\mathrm{H}}_{11}$${\mathrm{NH}}_{3}$]${\mathrm{CuBr}}_{3}$ (CHAB). This suggests that the soliton-phonon scattering in these systems is much smaller than in comparable antiferromagnetic systems, like tetramethylammonium manganese trichloride (TMMC).

Effect of diamagnetic doping on the magnetic resonance in a quasi-one-dimensional system tetramethylammonium manganese trichloride.

We present electron-spin-resonance data obtained on finite magnetic chains of ${\mathrm{CH}}_{3}$${\mathrm{NMn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$${\mathrm{Cl}}_{3}$ (TMMC-Cd) for x=0.02, 0.09, and 0.2. The measurements were developed with the microwave field either parallel or perpendicular to the magnetic field. The longitudinal relaxation time was also measured in the x=0.02 and 0.09 samples. All our experimental results show a noticeable influence of the impurities on both the line shape and linewidth, contrary to previously published data. New nuclear magnetic resonance data dealing with high-frequency proton relaxation rates are also presented. A full treatment using the memory-function formalism has been carried out to account for the significant difference observed between pure and doped samples. Our experimental data are satisfactorily described by this theory and the model of correlation functions for finite chains.

Theory of the soliton-induced phase transition in quasi-one-dimensional magnets.

It is shown that the phase transition occurring in quasi-one-dimensional systems of weakly coupled magnetic chains with solitons in the form of \ensuremath{\pi} kinks is closely related to the properties of these solitons. The critical behavior of the systems considered corresponds to the critical behavior of the Ising model with the same dimension. The model describing the behavior of solitons below and above the critical temperature is presented. This model explains the experimental field dependence of the magnetization direction in the spin-flopping configuration for antiferromagnetic ${\mathrm{K}}_{2}$${\mathrm{FeF}}_{5}$. Application of the theory proposed here to the antiferromagnetic tetramethylammonium manganese trichloride (TMMC) allows one to explain the experimental field dependence of the N\'eel temperature.

Kink-anti-kink scattering for an easy-plane one-dimensional antiferromagnet

A numerical investigation of collisions of kink-anti-kink (KK) pairs in an easy-plane classical antiferromagnetic chain is presented here, for the case of an applied field within the easy plane. An approximate kink profile as obtained from an earlier ansatz was used as the initial condition for numerical integration on a discrete lattice. As a function of the applied magnetic field and kink ansatz parameter theta A, which measures the tilt of the spins out of the easy plane, the authors have found distinct parameter regimes resulting in transmission, reflection, and annihilation of the KK pair. Results for both the in-plane (XY) and out-of-plane (YZ) kinks are summarised, and comparison is made to KK scattering in the easy-plane ferromagnet. Similarly to the case of the easy-plane ferromagnetic CsNiF3, it is found that these results imply difficulties in the interpretation of experiments on tetramethylammonium manganese trichloride (TMMC) in terms of classical soliton theory. For example, for fields from approximately 20 to 80 kG, the low-velocity XY collisions generally result in pair annihilation to spin waves. For fields less than 20 kG, however, the low-velocity KK XY pair transmit. Experimental results for TMMC are discussed in the light of these features.

One-dimensional exciton diffusion in a conjugated polymer.

One of the most interesting questions in modern transport theory has been and still is the following: What is the influence of dimensionality (including fractal) on the carrier and exciton dynamics and decay kinetics in quasiordered and disordered systems. An enormous amount of theoretical work has been done in this field, extended now to include direct computer simulations. Experimental data have been more difficult to find and are consequently sparse and not always convincing. Certain types of organic compounds and, in particular polydiacetylenes, constitute unique classes of nearly one-dimensional systems. Studies including photoconductive decays have been extended to include picosecond luminescence decay on PDA-1OH [poly(diacetylene-1-hydroxy-hexadyine-diol)], a continuous highly oriented fibrous polymer. The decay laws are compared with exact results in dimensionalities d=1 and near 1. The present data together with the recent work on doped tetramethylammonium manganese trichloride may be evidence for the first time of one-dimensional exciton motion.

Soliton dynamics in a magnetic chain. I. Antiferromagnet.

We study theoretically the effects of the soliton-soliton collision and the soliton-magnon collision in an antiferromagnetic chain in a magnetic field perpendicular to the chain direction. We find that the soliton-soliton collision flips the sign of the magnetization carried by solitons, which leads to the magnetization damping. In addition, the collision gives rise to soliton diffusion. The present theory accounts for the broadening of the parallel spin-correlation function of tetramethyl ammonium manganese trichloride recently observed by Boucher et al.

Brillouin scattering investigation of structural phase transitions in TMMC and TMMC:Cu

Structural phase transitions of tetramethyl ammonium manganese trichloride (TMMC) are investigated by using the Brillouin scattering method. The temperature dependences of the elastic coefficients C11 and C33 extracted from the experimental data are analysed by using the Landau theory of phase transitions. The step anomaly of C33 observed at the order-disorder transition temperature Tc can be attributed to a coupling between the order parameter and totally symmetric strains. An anomalous softening C33 above Tc indicates an interaction also between tetramethyl ammonium (TMA) molecules and the MnCl3 chains. A new lattice anomaly, which the authors attribute to a change in the rotational degree of freedom of the TMA molecules, is observed at about 395K. Doping of TMMC with 2% of Cu2+ creates a sequence of phases with transition temperatures at 92, 124 and 130K. An incommensurate phase stabilised by impurities may be involved in this sequence. Strong elastic scattering of light indicating a formation of needle-like domains along the c axis is observed in the doped crystals between 90 and 130K.

A neutron scattering investigation of some aspects of the structural phase transition in (CD3)4NMnCl3(TMMC)

A series of measurements on the nature of the order-disorder molecular phase transition at Tc approximately 126.5K in tetramethylammonium manganese trichloride (TMMC) is reported. These measurements involve the use of diffraction, diffuse elastic and quasistatic, and inelastic, coherent neutron scattering techniques. The transition is found to be driven by a strong coupling between the librational motion of the tetramethylammonium molecule and the TA (100) phonon mode. This coupling gives rise to quasielastic critical scattering at the low-temperature superlattice peak positions and to an over-damping of the phonon modes. Estimates of parameters involved in the coupled pseudospin-phonon theory of Yamada et al. (1974) are made from the nature of the spectrum near Tc. Below Tc the acoustic translational and librational modes become clearly resolved. Some observations on the nature of the low-temperature structure are given.

Erratum: New method for calculating transport coefficients and application to the Heisenberg chain

In this article, a new simple method to calculate memory functions within the Mori formalism is presented. It is then used to derive the relaxation function for a Heisenberg chain. The results for different choices of relevant variables are compared with experiments and other theories. It is found that for the right choice of variables, the results are in much better agreement with recent experiments on tetramethylammonium-manganese-trichloride (TMMC) than the results of other theories.

Half-field EPR transition in the one-dimensional paramagnet tetramethylammonium-manganese-trichloride (TMMC)

We report the observation of a half-field transition in the EPR spectrum of tetramethylammonium-manganese-trichloride (TMMC). The observation of this new resonance is a direct consequence of the one-dimensionality of the spin dynamics of this manganese salt. We present a theory which accounts for many of the observed features in a very satisfactory way. The experiments are performed with the microwave field parallel to the static magnetic field. The most important characteristics of the transition are the scaling of the linewidth with the EPR spectrum obtained with the microwave field perpendicular to the static magnetic field, and its highly anisotropic intensity.

New method for calculating transport coefficients and application to the Heisenberg chain

In this article, a new simple method to calculate memory functions within the Mori formalism is presented. It is then used to derive the relaxation function for a Heisenberg chain. The results for different choices of relevant variables are compared with experiments and other theories. It is found that for the right choice of variables, the results are in much better agreement with recent experiments on tetramethylammonium-manganese-trichloride (TMMC) than the results of other theories.

Specific heat of nearly-one-dimensional tetramethyl ammonium manganese trichloride (TMMC) and tetramethyl ammonium cadmium trichloride (TMCC)

The specific heat of tetramethyl ammonium manganese trichloride and its cadmium isomorph is measured for $2<T<52$ K. The temperature dependence of the lattice specific heat of the cadmium compound could be fitted with an expression based upon a pseudoelastic approach of the lattice vibrations in this low-dimensional system. Application of this approach to the manganese compound yields a magnetic contribution which fits the overall behavior of a one-dimensional Heisenberg model with an intrachain interaction of $\frac{J}{k}=\ensuremath{-}6.7\ifmmode\pm\else\textpm\fi{}0.5$ K. Inspection of the low-temperature region yields a satisfactory agreement with the expression ${C}_{m}=1.1|\frac{\mathrm{kT}}{J}|+0.5{|\frac{\mathrm{kT}}{J}|}^{2}\ensuremath{-}0.13{|\frac{\mathrm{kT}}{J}|}^{3}$, predicted by recent calculations.

Linear-Chain Antiferromagnetism in [(CH3)4N] [MnCl3

This paper reports optical and magnetic properties of tetramethyl ammonium manganese trichloride, [${(\mathrm{C}{\mathrm{H}}_{3})}_{4}$N][Mn${\mathrm{Cl}}_{3}$]. Magnetically, the system is one of very weakly interacting chains of ${\mathrm{Mn}}^{++}$ ions. Magnetic-susceptibility measurements are given from room temperature to below 1\ifmmode^\circ\else\textdegree\fi{}K and show a possible phase transition at 0.84\ifmmode^\circ\else\textdegree\fi{}K. Theoretical analysis reveals that the system approximates very closely a Heisenberg linear-chain antiferromagnet with interchain interactions many orders of magnitude smaller than intrachain exchange $J$. We find $J=6.3\ifmmode^\circ\else\textdegree\fi{}$K and a susceptibility maximum at 55\ifmmode^\circ\else\textdegree\fi{}K. The optical spectrum shows certain features that are not easily accounted for by an isolated Mn${\mathrm{Cl}}_{6}$ cluster, and may contain information concerning the nature of low-temperature dynamics of the Heisenberg linear chain, although no positive identification of magnon sidebands has yet been made.