Electron spin resonance line shapes for one- and two-dimensional random walk processes

Tang, Jau; Dikshit, S. N.; Norris, James R.

doi:10.1063/1.470500

Cited by 24 publications

(20 citation statements)

References 24 publications

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“…Figure 5a shows the transverse relaxation processes of the gl and g2 canonical field positions measured at 45 K. At this temperature, a prominent effect of the soliton diffusion was observed at X-band [18]. The transverse relaxation curves measured at W-band also exhibited nonexponential decays, characteristic of a onedimensional random walk [28]. However, the relaxation curve along the g~ canonical field is almost identical to that along the g2 field.…”

Section: Resultsmentioning

confidence: 93%

Angle-selective measurements of spin soliton in ladder polydiacetylene by pulsed 94 GHz EPR

et al. 2003

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Angle-selection experiments of a spin soliton in randomly oriented ladder polydiacetylene were carried out by pulsed electron paramagnetie resonance (EPR) at W-band. EPR measurement using 94 GHz mierowaves increased the difference in the resonance field due to g anisotropy of the spin soliton to allow the orientation dependence of transient nutation, electron nuclear double resonance (ENDOR) and spin relaxations to be investigated. The shape of the g anisotropy-resolved nutation spectrum was discussed on the basis of the EPR transition moments and the differences between spin relaxation times. Reliable assignments of hyperfine couplings to the [3 protons (HI3) of the alkyl side chains were achieved with the support of W-band ENDOR measurements. No significant orientational dependence in the Tt and T z processes was found in terms of isotropy of the H~-hyperfine interaction.

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Section: Resultsmentioning

confidence: 93%

Angle-selective measurements of spin soliton in ladder polydiacetylene by pulsed 94 GHz EPR

et al. 2003

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“…The first experimental confirmation of spin diffusion was done in a Heisemberg AFM spin chain containing Mn ions [27,28]. It should be further noted that in a spin ring or a short spin segment the CF, after an initial fast decay due to the AFM exchange interaction, reaches a constant value inversely proportional to the number N of spins, as long as the total spin value is conserved [29,30]. In both the infinite and in the finite chain or ring the CF eventually goes to zero due to anisotropic terms in the spin-spin interaction which do not conserve the total spin.…”

Section: Room Temperature Nmr Results and Discussionmentioning

confidence: 99%

“…The time at which the CF decays to zero is called cutoff time. If we refer to the spectral density (i.e., the Fourier transform of the CF), the cutoff frequency is the frequency at which the low-frequency enhancement of S(ω) levels off [27][28][29][30].…”

Section: Room Temperature Nmr Results and Discussionmentioning

confidence: 99%

NMR Study of Spin Dynamics in V7Zn and V7Ni Molecular Rings

et al. 2020

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We present a 1H NMR investigation of spin dynamics in two finite integer spin molecular nanomagnetic rings, namely V7Zn and V7Ni. This study could be put in correlation with the problem of Haldane gap in infinite integer spin chains. While V7Zn is an approximation of a homometallic broken chain due to the presence of s = 0 Zn2+ ion uncoupled from nearest neighbor V2+s = 1 ions, the V7Ni compound constitutes an example of a closed periodical s = 1 heterometallic chain. From preliminary susceptibility measurements on single crystals and data analysis, the exchange coupling constant J/kB results in the order of few kelvin. At room temperature, the frequency behavior of the 1H NMR spin–lattice relaxation rate 1/T1 allowed to conclude that the spin–spin correlation function is similar to the one observed in semi-integer spin molecules, but with a smaller cutoff frequency. Thus, the high-T data can be interpreted in terms of, e.g., a Heisenberg model including spin diffusion. On the other hand, the behavior of 1/T1 vs temperature at different constant fields reveals a clear peak at temperature of the order of J/kB, qualitatively in agreement with the well-known Bloembergen–Purcell–Pound model and with previous results on semi-integer molecular spin systems. Consequently, one can suggest that for a small number N of interacting s = 1 ions (N = 8), the Haldane conjecture does not play a key role on spin dynamics, and the investigated rings still keep the quantum nature imposed mainly by the low number of magnetic centers, with no clear topological effect due to integer spins.

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“…To estimate the diffusion rate of the soliton, we have analyzed the ESE decay with a model for a one-dimensional random-walk process. 58 Here, we assume that within an infinite polymer wire soliton, hopping takes place only between nearest-neighbor sites and that the hopping rate constant k d is much larger than 1/t. According to Kubo and Tomita's formalism, 59 the response function S(t) is expressed as…”

Section: Spin Dynamicsmentioning

confidence: 99%

Spin soliton in aπ-conjugated ladder polydiacetylene

et al. 2002

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The electronic structure and the spin dynamics of a spin soliton observed in a ''ladder''-structured polydiacetylene have been investigated using multifrequency pulsed and continuous-wave ͑cw͒ electron paramagnetic resonance ͑EPR͒, electron spin echo ͑ESE͒ spectroscopy, electron-nuclear double resonance ͑ENDOR͒, and electron-nuclear-nuclear triple resonance ͑TRIPLE͒. The undoped ladder polymer in which two polydiacetylene wires are linked by bridges consisting of two triple bonds exhibits a strong EPR signal. In contrast, no EPR signal is observed in the ladder-structured polydiacetylene, where the bridges consist of single bonds. The observed bridge effect on the probability of formation of paramagnetic centers is interpreted in terms of a quasidegenerate ground state due to the -conjugated ladder structure that creates a -bond kink corresponding to a spin soliton. High-frequency and high-field EPR reveals a small anisotropy of the g tensor ͑principal values g 1 ϭ2.0037, g 2 ϭ2.0028, and g 3 ϭ2.0023) for the spin soliton. By nutation spectroscopy, the spin multiplicity was confirmed to be Sϭ1/2. The hyperfine pattern attributed to the ␤ protons was detected by ENDOR and TRIPLE methods, providing evidence for both the positive and negative spin densities of the soliton wave function. These experimental results led to the conclusion that the unpaired electron of the spin soliton was substantially delocalized over the two polydiacetylenes through the -conjugation. At temperatures ͑T͒ below 50 K, the width of the EPR spectrum narrows by about 45% with increasing temperature and the width remains nearly constant for TϾ50 K. The pronounced change in the line width for TϽ50 K suggests the presence of a mobile spin soliton in the ladder-structured polydiacetylene. A temperature dependence of the electron spin system's phase memory time T M for TϽ50 K was also observed by ESE spectroscopy. The decay of the ESE exhibits a nonexponential behavior, with T M increasing monotonically with rising temperature. These findings represent clear experimental evidence for motional narrowing phenomena. Based on a onedimensional random-walk model for the unpaired electron spin along the ladder polymer, the soliton's diffusion rate constant was estimated from an analysis of the ESE dephasing process. An Arrhenius plot of the diffusion rate was asymptotic to Ϸ8ϫ10 7 s Ϫ1 at very low temperature, which is two orders of magnitude slower than that of the soliton in trans-polyacetylene.

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Electron spin resonance line shapes for one- and two-dimensional random walk processes

Cited by 24 publications

References 24 publications

Angle-selective measurements of spin soliton in ladder polydiacetylene by pulsed 94 GHz EPR

Angle-selective measurements of spin soliton in ladder polydiacetylene by pulsed 94 GHz EPR

NMR Study of Spin Dynamics in V7Zn and V7Ni Molecular Rings

Spin soliton in aπ-conjugated ladder polydiacetylene

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