Soliton Contribution to the Mössbauer Linewidth in Quasi-One-Dimensional Antiferromagnets with Ising Anisotropy: Theory Versus Experiment

Abstract

A discussion is given of the contribution to the Mossbauer linewidth in quasi-one-dimensional antiferromagnets with Ising anisotropy due to thermal excitation of moving domain walls ("kinks" or "solitons"). Experimental data on Fe 2+ chain compounds are presented that confirm the predicted exponential temperature dependence of the linewidth.PACS numbers: 76.80.+y, 76.60.Es, 75.10.Hk The study of solitary excitations is an exciting new topic that has an impact on a great many branches of physics. 1 In contrast to the rapid development of theoretical understanding of nonlinear dynamics, very few experimental results bearing upon this problem have been obtained up till now. It is therefore of great importance to find new ways in which to probe the presence of these nonlinear excitations and to establish their influence on experimentally measurable quantities.It has recently become apparent that magnetic chains offer quite promising possibilities in this respect. Following a suggestion of Mikeska, 2 an inelastic neutron scattering study on the quasione-dimensional (ID) XY ferromagnet CsNiF 3 was performed by Kjems and Steiner, 3 who found an anomalous increase in intensity of the central peak attributed to scattering of the neutrons by the solitons.It has subsequently been shown, 4 that analogous local excitations exist in a ID XY antif erromagnet. In a series of field-dependent neutron inelastic scattering and NMR studies on (CH 3 ) 4 NMnCl 3 (TMMC), contributions ascribed to solitons have been observed which were very much more pronounced than those found in CsNiF 3 .It is the purpose of this note to point out that Mossbauer spectroscopy can provide an additional tool for studying such nonlinear excitations. Similarly to NMR, the Mossbauer effect measures the hyperfine interaction between electronic and nuclear spins. Spin fluctuations arising from linear as well as from nonlinear excitations may contribute to the Mossbauer linewidths, just as they contribute to the NMR nuclear spin lattice relaxation time T im After a brief outline of the formal analogy between the Mossbauer linewidth F, the 1/T 1 in NMR, and the neutron scattering cross section, we present experimental linewidth data on a number of linear chain Fe 2+ antiferromagnets with different Ising-type spin anisotropy. In this class of soliton-bearing systems solitons have not been studied before experimentally. Because of the Ising type of anisotropy there is no need for a symmetry-breaking applied magnetic field. 5 The contribution to r from the solitons reveals itself as an anomalous line broadening that extends to temperatures far above the 3D magnetic ordering temperature T c (brought about by the weaker interchain couplings), and shows an exponential dependence on temperature.In theoretical treatments of spin fluctuations, one considers the space-time correlation between spins via the pair correlation functions G aa (r,t) = (S a (r,t)S a (0,Q)).By taking the space-time Fourier transform of G aa (r,t), the dynamical structure factor (Van Hove scatt...

Magnetic Susceptibility Calculated from Correlation-Lengths Derived by Mössbauer Relaxation Spectra

“…Above 13 K, the intensity of the slowly relaxing subspectrum becomes negligible, such that only a single spectrum is sufficient to fit the experiment. These features were in common for all our samples studied by Mössbauer spectroscopy and were also observed by de Jongh and his group [16][17][18]. The Mössbauer spectra were assumed to consist of two subspectra with equal static parameters but different relaxation rates.…”

“…From the analysis of Mössbauer relaxation spectra based on the classical soliton model [13][14][15][16][17][18] we were able to determine the activation energy for such a soliton from the temperature dependence of the spin-fluctuation rate in the antiferromagnetic 1-d phase even of powder samples [8-10, 12, 19-21].…”

Exact soliton solution of spin chain with an external magnetic field in linear wave background

“…Soliton in quasi one-dimensional magnetic systems is no longer a theoretical concept but can be probed by neutron inelastic scattering [5,6], Mossbauer linewidth measurements [7], and electron spin resonance [8]. One of the integrable models for spin chain is Landau-Lifshitz equation [9] which has been studied by a variety of techniques such as inverse scattering transformation [3,10,11], Darboux transformation [12], Riemann-Hilbert approach [13], etc.…”

Exact soliton solution and inelastic two-soliton collision in a spin chain driven by a time-dependent magnetic field

“…The classical Heisenberg spin chain which exhibits both coherent and chaotic structures depending on the nature of the magnetic interactions [1][2][3][4] has attracted considerable attentions in nonlinear science and condensed-matter physics. Solitons in quasi one-dimensional magnetic systems have already been probed experimentally by neutron inelastic scattering [5,6], nuclear magnetic resonance [7,8], Mossbauer linewidth measurements [9], and electron spin resonance [10]. The corresponding theoretical studies are based usually on the Landau-Lifshitz equation [11].…”