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Getting to a higher level. Terrace fields in Tipón, Cuzco Department, Peru. (photo: A. Ruebenbauer) |
Early scientific activity was concentrated on the investigation of the coexistence of the ferromagnetism and superconductivity in magnetically diluted rare earth systems. A region of coexistence of the magnetically soft ferromagnetic clusters embedded in a superconducting matrix has been found in Gd_{x}Ce_{1-x}Ru_{2} Laves phase by means of the ^{155}Gd Mössbauer spectroscopy [1]. Hence, it was shown that the second critical magnetic field might be quite strong locally. This finding was later confirmed by the discovery of high temperature superconductors by Bednorz and Müller.
A work on the highly sophisticated Mössbauer data processing software was started in late seventies [2]. This work has been continued over many years resulting in the MOSGRAF package being used in our laboratory and many worldwide leading Mössbauer laboratories.
It was shown that for a space-time exhibiting quantum fluctuations on the Planck's length/time scale infinitely "narrow" spectral lines do not exist [3]. Relative broadening scales linearly with the average frequency of the photon. Unfortunately, it is too small to be observed by the current technology.
Magnetically diluted Heusler-type alloys have been investigated by means of the Mössbauer spectroscopy in order to answer quite fundamental question how far from the more or less localized magnetic moment extends polarization of the conduction band. It was found that the polarization decays quite rapidly with the distance [4,5], and hence such models like RKKY do not apply. On the other hand, one can interpret coupling in terms of the models involving strong hybrydization of the valence electrons.
Several setups of the vibrating magnetometer have been designed allowing to measure all components of the susceptibility tensor without reorienting sample, i.e., in a single experimental run [6]. Setups have been optimized for the signal to noise ratio.
A series of papers has been devoted to the investigation of the diffusional correlation functions in various lattices [7-12]. The Monte-Carlo method has been extensively used to look upon mono- and divacancy mechanisms in cubic lattices. Similar methods have been applied to hexagonal lattices with the particular attention paid to the determinableness of the observables from the experimental data. A high temperature emission Mössbauer spectroscopy has been mastered resulting in the pioneering measurements of the cobalt/iron diffusivity in beryllium by means of the emission Mössbauer spectroscopy [12]. Emission Mössbauer spectroscopy at high temperatures and under various atmospheres is still the main experimental activity of our laboratory.
Investigations of the anisotropy of the recoilless fraction focused attention as well [13-15]. Detailed examinations of the above anisotropy have been performed on the low symmetry crystal of stannous fluoride by means of neutron diffraction and compared with the observed Goldanskii-Karyagin effect on the random powder samples investigated by means of the Mössbauer spectroscopy [13]. Results have been found to be consistent. A general theory describing Goldanskii-Karyagin effect has been outlined [14]. A special method allowing to look upon recoilless fraction anisotropy in amorphous materials has been invented [15]. It relies upon application of the strong external magnetic field parallel to the Mössbauer beam within the absorber volume. It is successful provided a local non-scalar hyperfine interaction is present. The basic idea of the above method is shown in Fig. 1. Investigations of the recoilless fraction anisotropy are continued in our laboratory by various methods. The software package MOSGRAF contains all tools to deal with the above anisotropy up to the quartic order. A set of programs to deal with the external magnetic field method is a part of MOSGRAF. It allows to go beyond the original setup, i.e., to work with split and eventually polarized source and to work with a field oriented at an arbitrary angle versus the beam.
Fig. 1. The basic idea of the external magnetic field method to look upon anisotropy of the recoilless fraction. Note, the transformation of the molecule A into B changes the sign of the axial electric field gradient tensor.
[ 1] | K.Ruebenbauer, J.Fink, H.Schmidt, G.Czjzek, and K.Tomala, An investigation of magnetic ordering in Gd_{x}Ce_{1-x}Ru_{2} by ^{155}Gd Mössbauer spectroscopy, Phys.Stat.Solidi B 84, 611-618 (1977). |
[ 2] | K.Ruebenbauer and T.Birchall, A computer programme for the evaluation of Mössbauer data, Hyp.Int. 7, 125-133 (1979). |
[ 3] | K.Ruebenbauer, Some consequences of the non-localizability of the space-time events, Int.J. Theoretical Physics 19, 185-187 (1980). |
[ 4] | T.Birchall, K.Ruebenbauer, and C.Stager, A ^{119}Sn Mössbauer spectroscopic investigation of the Pd_{2}Mn_{x}V_{1-x}Sn system, Phys.Stat.Solidi A 59, 347-353 (1980). |
[ 5] | K.Ruebenbauer, ^{119}Sn Mössbauer spectroscopy in the magnetically diluted Heusler-type systems, INP Report 1133/PS (1981). |
[ 6] | A.W.Pacyna and K.Ruebenbauer, General theory of a vibrating magnetometer with extended coils, J.Phys.E: Sci.Instr. 17, 141-154 (1984). |
[ 7] | K.Ruebenbauer, Evaluation of diffusion broadened Mössbauer spectra in single crystals of FCC metals, Hyp.Int. 14, 139-157 (1983). |
[ 8] | K.Ruebenbauer and B.Sepiol, Systematic investigation of self-correlation functions in cubic lattices; mono- and divacancy mechanisms, Springer Proceedings Phys. 10, 139-142 (1986). |
[ 9] | K.Ruebenbauer and B.Sepiol, Self-correlation functions for impurity diffusion in cubic lattices, Hyp.Int. 30, 121-134 (1986). |
[10] | B.Miczko, K.Ruebenbauer, and B.Sepiol, Self-correlation functions for impurity diffusion in hexagonal lattices, Hyp.Int. 52, 107-121 (1989). |
[11] | K.Ruebenbauer, B.Sepiol, and B.Miczko, Determinableness of the reduced frequencies from the observable diffusional self-correlation functions, Physica B 168, 80-84 (1991). |
[12] | B.Sepiol, K.Ruebenbauer, B.Miczko, and T.Birchall, Mössbauer study of iron diffusion in beryllium, Physica B 168, 159-162 (1991). |
[13] | T.Birchall, G.Dénès, K.Ruebenbauer, and J.Pannetier, Goldanskii-Karyagin effect in alpha-SnF_{2}: A neutron diffraction and Mössbauer absorption study, Hyp.Int. 30, 167-183 (1986). |
[14] | K.Ruebenbauer, Goldanskii-Karyagin effect in the absence of inversion centres, Physica B 172, 346-354 (1991). |
[15] | K.Ruebenbauer and B.Sepiol, Goldanskii-Karyagin effect and external magnetic field method as tools to measure anisotropy of the recoilless fraction in amorphous materials, Hyp.Int. 23, 351-374 (1985). |