H.H.A. Smit

155Gd Mössbauer measurements on the ceramic superconductor GdBa2Cu3O7

Abstract 155Gd Mossbauer effect measurements have been performed on GdBa2Cu3O7 both in the superconducting orthorhombic and in the semiconducting tetragonal phase. The observed isomer shifts are similar to those found in insulating Gd-transition metal-oxides, indicating that there is no conduction electron density within the Gd layers Below the temperature at which the specific heat shows a sharp peak both phases show magnetic ordering. The Gd moment is found to be parallel to the c-axis. Dipolar calculations show that the dipolar field at the Cu sites is negligibly small and that the magnetic ordering of the Gd moments is probably of the 2-d Ising type.

Physical properties of metal cluster compounds IV: The thermal motion of the Au55-core in Au55(PPh3)12Cl6 as probed by 197Au Mössbauer spectroscopy

Abstract We have performed 197Au Mossbauer Effect Spectroscopy (MES) on the title compound as a function of temperature, obtaining information on the vibrational motions of the four distinct Au-sites, as well as of the cluster as a whole. The results are compared to earlier MES work on colloidal gold clusters and to LEED experiments on metallic gold surfaces.

Physical properties of high-nuclearity metal cluster compounds

Metal cluster compounds are composed of large macromolecules, which consist of a metal core (cluster) containing a certain number (n=6–560) of metal atoms, to which core a shell of ligands is coordinated. They provide excellent model systems for an assembly of identical metal clusters, embedded in a dielectric matrix. We discuss a number of physical properties of these materials.

Mössbauer and specific heat studies of the vibrations of metal core atoms in polynuclear gold cluster compounds

Abstract 197Au Mossbauer effect spectroscopy and specific heat measurements have been performed as a function of temperature on the three gold polynuclear cluster compounds [Au9[PPh3)8](NO3)3, Au11(PPh3)7(SCN)3, and Au55(PPh3)12Cl6. The Mossbauer data yield information on the vibrational motions of the various distinguishable Au sites, as well as on the motion of the clusters as a whole. The Mossbauer and the specific heat data are successfully described by a superposition of inter- and intra-cluster vibrations. The latter are determined by calculating numerically the normal modes of vibration of the metal cores.

Mössbauer relaxation studies of non-linear dynamical excitations in low-dimensional magnets

Mössbauer effect spectroscopy provides an excellent probe to study domain wall dynamics in the quasi 1-d Ising-type magnetic chain. Theoretical aspects of moving domain walls (nonlinear excitations, kinks, solitons) are briefly discussed, both for quantum and classical 1-d systems. We review experimental data on Fe(N2H5)2(SO4)2, RbFeCl3·2H2O and FeCl2 (NC5H5)2. Analysis of the spectra is performed in two different ways: by extracting linewidths, and by fitting to the Blume-Tjon relaxation model, which is argued to give the exact description for the Mössbauer spectrum of a magnetic chain, subject to free-kink behaviour. Differences between this theory and experiments are discussed.

Field-dependent Mössbauer relaxation study of domain walls in the quasi 1-d antiferromagnet RbFeCl3.2H2O

Abstract Domain walls (narrow solitons) in the Ising-type quasi 1-d antiferromagnet RbFeCl3.2H2O have been studied by means of Mossbauer relaxation experiments in magnetic fields strong enough (1.5 T) to suppress the 3-d long-range ordering. Excellent agreement is obtained with the Blume - Tjon model, assuming stochastic relaxation due to the propagation of wall- pairs . In still higher fields (6 T) the excitation of walls is found to be suppressed by the generation of a staggered field on the (slightly canted) antiferromagnetic chains.

The thermal motion of gold atoms in metal cluster compounds as determined by Mössbauer and specific heat

197Au Mossbauer effect spectroscopy and specific heat measurements have been performed as a function of temperature on three gold polynuclear cluster compounds, [Au9(PPh3)8](NO3)3, Au11(PPh3)7(SCN)3, and Au55(PPh3)12Cl6. The Mossbauer data yield information on the vibrational motions of the various distinguishable Au sites, as well as on the motion of the clusters as a whole. The Mossbauer and the specific heat data are successfully described by a superposition of inter- and intra-cluster vibrations. The latter are determined by calculating numerically the normal modes of vibration of the metal cores.

Application of Mössbauer Effect Spectroscopy to Cluster Research

During the course of the last 35 years, Mossbauer Effect Spectroscopy (MES) has been well established as a powerful measurement technique in both solid state physics and chemistry [1, 2, 3, 4, 5]. Because of the existence of so many excellent reviews of MES, we will only give a brief sketch of the basics needed to understand the use of the technique, in particular as applied to cluster research.

Relaxation Phenomena in Non-linear Systems; A Mössbauer Effect Spectroscopy and Susceptibility Study

In the last few years our group has been engaged in a systematic study of the dynamics of kinks (solitons) in magnetic chain systems by means of Mossbauer Effect Spectroscopy (MES). In this paper we report on the progress made since the San Miniato dConference /l/, as well as on very recent frequency-dependent susceptibility studies /2/, which have greatly contributed to our understanding of the problems involved.