Regional Groups of Mössbauer Researchers - Hungary
Reprinted from the April 2003 edition of the Mössbauer Spectroscopy Newsletter, published as part of Volume 26, Issue 4 of the Mössbauer Effect Reference and Data Journal
Mössbauer Spectroscopy in Hungary
In the response to a general call for information on the current Mössbauer research that is taking place in Hungary, the following reports were received by the Mössbauer Effect Data Center.

Remembering the Early Years of Mössbauer Effect Studies in Hungary

L. Keszthelyi

Institute of Biophysics, Biological Research Centre
Hungarian Academy of Sciences
Szeged

Science could somewhat develop in Hungary in the years 1958-60, though we still felt the consequences of the 1956 revolution. In the Central Research Institute for Physics, we had accelerators of about 1 MeV energy and a nuclear reactor. We made some nuclear physics research and published papers, but were cut off from personal contacts with colleagues from Western countries. To compensate for this difficulty, we studied the literature that, luckily enough, arrived without restriction. Thus, I found the paper of Rudolf Mössbauer and became enthusiastic. I became even more so when I read the paper of Pound and Rebka on the 57Fe Mössbauer effect. It was easy to understand that the study of the 57Fe Mössbauer effect offered immense possibilities to make studies in physics, chemistry, and so on. I realized that the Mössbauer effect opened a way for poor men’s physics. I wrote a letter to Rudolf Mössbauer expressing my views on the perspectives of this research, which were confirmed in his answer.

It was obvious that the study of the 57Fe Mössbauer effect should be a program in our laboratory. There were, however, two problems. First, the apparatus to move the source or absorber to a vibration-free place. I thought this would be easy because we had good technicians, but it turned out to be difficult, as I came to understand in the coming years. Second, we had to buy 57Co isotope from a "capitalist" country because our accelerators and the reactor could not produce it. It seemed impossible. Nevertheless, we ordered the isotope and, as a wonder, we obtained it in October 1960. István Dézsi, a nuclear chemist, was at hand and wanted to join the program. The technicians fabricated a rotating cam to move the source with one velocity in one direction. Dézsi diffused the isotope into iron foil that was attached to the mover. I remember that on a misty November night, Dézsi and I began to measure the number of transmitted γ-quanta through iron foil, changing the frequency of the rotation step-by-step. We were extremely happy seeing that we reproduced the results known to us from literature. Our happiness culminated on the 5th of December, when we took all our apparatus to the usual Monday night meeting of the Roland Eötvös Physical Society and demonstrated the 57Fe Mössbauer effect for the physics community in Budapest. (Just to characterize the circumstances, I mention that an agent of the Hungarian Secret Police with a cover name reported that I delivered a lecture in the physicist’s club on ….. effect. I learned that in this year, 2003, when I obtained the secretly collected information about my activities.) In 1961, I wrote a paper in Hungarian to show the possibilities of the Mössbauer effect [1].

After the euphoria, we had to continue our work to do real research. The rotating cam was not a productive apparatus; therefore, we asked our engineers to build a machine based on oil pressure that could produce positive and negative velocities. That was made, but oil came out everywhere. We worked with that and reported some not very interesting results in Hungarian [2].

Our first notable outcome was a report on the Mössbauer effect of 159Tb nuclide. We reported preliminary measurements at the Mössbauer meeting in Dubna [3]. A more thorough paper was published in 1966 [4] when, due to the effort of the engineers of the Central Research Institute of Physics, we already had a "modern" Mössbauer apparatus with the source attached to the coil of a loudspeaker and multichannel analyzer for data collection. Everything, even the multichannel analyzer, was manufactured in our workshop. The first apparatus was ready in early 1964 and later became a product, and was sold inside Hungary and also exported, for example, to Egypt.

It took nearly four years to reach a satisfactory level of experimentation. Our first really interesting work was made in 1964 when, following the suggestion of István Dézsi, we measured the Mössbauer effect on iron salts in ice [5]. The data were surprising, but also rewarding because this paper catalyzed an important sub-topic inside Mössbauer effect studies.

"Poor men’s physics" attracted many good people into our group: László Cser, Dénes Nagy, and Imre Vincze were the first to join us. Work started also at the Eötvös Loránd University, where László Korecz, Attila Vértes, and Kálmán Burger dealt with the Mössbauer effect. We had long-term visitors from East Germany (Werner Meisel, Klaus Fröhlich), from Poland (Dominik Kulgawczuk, Jozef Bara), from Egypt (Nabil Eissa, Ahmed Sanad), and others. The activity brought worldwide acknowledgement: we were entrusted to organize the International Conference on the Mössbauer Effect in 1969.

My personal career took another way in 1973, when I accepted a position in the Institute of Biophysics, Biological Research Centre of the Hungarian Academy of Sciences. My first interest in biophysics – the search of the origin of homochirality of biomolecules – was not too far from my physics background. Homochirality of biomolecules means that all living beings contain L-amino acids and D-sugars, though by synthesis both are produced in equal number. One of the ideas – to trace the origin of this asymmetry – was that the circularly polarized bremsstrahlung, produced by the β-particles, could destroy the D-amino acids. We thought with Imre Vincze to check this assumption with the circularly polarized lines from magnetic splitting of 57Fe. We found that the relative difference in absorption of 14 keV γ-radiation between L- and D-amino acid is less than 10-4 [6].

The development in physics led to another important application of the Mössbauer effect in the same field. It turned out that, due to weak neutral current, an energy difference exists between L-and D-molecules. The difference, calculated theoretically, is very small, but it increases with the 6th power of Z of atom in the asymmetry center. I thought that the extremely high resolution of the Mössbauer effect offers a method to measure this basic phenomenon. Kálmán Burger and Attila Vértes helped to organize L- and D- Ir complex from Denmark (F. Galsbøl and B. Rasmussen) and measuring capacity from Germany (F. Wagner). The isomer shift was supposed to reflect the difference of the energy between the two complexes. An upper limit could only be established: the difference in isomer shift is surely smaller than 3.8 x 102 times the theoretical value [7]. Recently, I figured out that the difference, if at all, could be measured in case of 181Ta nuclide [8].

The two last paragraphs do not belong to the first years of Mössbauer studies in Hungary. I included them only to demonstrate that what I learned in the field of the Mössbauer effect reappeared in my mind encountering another problem. Thus, my early enthusiasm comes back even in these days – in my work and also in the work of a large number of people in the Hungarian Mössbauer community.

References

  1. L. Keszthelyi, "Mössbauer effect and its applications" (in Hungarian). Magy. Fiz. Folyóirat 9, 2891 (1961).
  2. I. Demeter, I. Dézsi and L. Keszthelyi, "Measurements with the aid of Mössbauer effect" (in Hungarian). KFKI Közl. 10, 21 (1962).
  3. I. Dézsi and L. Keszthelyi, "Observation of the Mössbauer effect in Tb159." In Proc. Dubna Conf. on Mössbauer Effect (in Russian), 857 (1963).
  4. T. Czibók, I. Dézsi and L. Keszthelyi, "Mössbauer-effect in Tb159." Acta Phys. Hung. 20, 3791 (1966).
  5. I. Dézsi, L. Keszthelyi, L. Pócs and L. Korecz, "Mössbauer-effect on some iron salt in ice." Phys. Letters 14, 1411 (1965).
  6. L. Keszthelyi and I. Vincze, "Absorption of circularly polarized γ-radiation in L- and D- amino acids." Rad. Environm. Biophys. 12, 181 (1975).
  7. L. Keszthelyi, J. Biol. Phys. 20, 241 (1994).
  8. L. Keszthelyi, Mendeleev Journal (2003), in press.

Mössbauer Groups of the KFKI Research Institute for Particle and Nuclear Physics (KFKI RMKI)
Budapest

I. Dézsi and D.L. Nagy
Department of Nuclear Physics
KFKI Research Institute for Particle and Nuclear Physics
Budapest

From Left to Right: L. Bottyán, M. Major, I.S. Szucs, I. Dézsi, B. Molnár, F. Tanczikó, Zs. Kajcsos, D.L. Nagy, Cs. Fetzer, D. Merkel, L. Deák, E. Szilágyi, J. Fenyves.

Mössbauer studies in Hungary were started by L. Keszthelyi and I. Dézsi in 1960. In November of this year, the effect on 57Fe was observed and presented. We intended to discover a new Mössbauer nucleus by choosing 159Tb. Using a 159Gd source prepared in the research reactor of the predecessor institute KFKI, the effort was successful. We observed first the Mössbauer transition on this nucleus [1]. After developing a reliable driving system, a series of studies was commenced on frozen solutions, alloys, and on transitional metal oxides. For frozen solutions, the studies yielded the first evidence of a glass transition, melting, recrystallization of the amorphous frozen solute-solvent system [2]. Detailed studies of the paramagnetic relaxation phenomena of Fe3+-containing solutions were carried out. Furthermore, systematic studies were performed on iron oxides, on α-FeOOH, δ-FeOOH, and (FeRh)2O3, as well as on perovskites. During the 1960s, successful international collaborations were begun and new colleagues – physicists L. Cser (1963), L. Korecz (1963), T. Czibók (1965), D.L. Nagy (in 1966 he became a member of our research group), I. Vincze (1967), and the chemist Attila Vértes (1966) – joined us to learn the Mössbauer effect. Together with Attila Vértes, we first showed the possible application of the Mössbauer effect for corrosion studies. Later on, intensive studies were made on high-spin ferrous hydrates and on organometallic complexes. Amongst the results obtained, the first Mössbauer evidence on the spin-crossover transition in Fe2+ compounds [3] and of an orbital ground state inversion in Fe2+ crystalline hydrates were discovered. The research reactor made it possible to perform Mössbauer experiments on various nuclides, such as 161Dy and 191Au. In 1969, we organized the first Mössbauer Conference where scientists both from the "Eastern" and "Western" countries participated [4].

In the early 1970s we continued studies, mostly in international collaboration (University of Louisville, Kentucky, USA, with P.J. Ouseph; Universität Erlangen, with H. Wegener and G. Ritter), on frozen solutions and crystalline hydrates. There was a successful collaboration between J.M.D. Coey and I. Dézsi in the studies of crystalline hydrates and magnetic oxides. Magnetic phase transitions in oxides, nitrides, and carbides were also studied, both with 57Fe and 119Sn resonance, the latter revealing a series of magnetic phase transitions in Mn3SnN and Mn3SnC. Soon thereafter, L. Keszthelyi’s interest turned to biophysics and Mössbauer spectroscopy no longer belonged to his applied methods. The research was extended by four new topics: the determination of texture parameters in Mössbauer absorbers, paramagnetic relaxation phenomena in crystalline systems containing high-spin Fe3+, catalysts containing Fe and LiNbO3 with Co and Fe impurity. The latter topic was studied in collaboration mostly with W. Keune and U. Gonser.

The investigation of ion-implanted systems began in the Instituut voor Kern- en Stralingsfysika of the Katholieke Universiteit Leuven with R. Coussement, G. Langouche, and M. Van Rossum in 1976. These studies resulted in the proof of the formation of amorphous regions in Si, Ge, substrates around the implanted 57Co, 57Fe, 125Te, 129I. It was also pointed out that CoSi2 forms in Co implanted and annealed Si. This silicide became one of the most important materials in semiconductor technology. The studies were also extended to the 133Cs nucleus in collaboration with H. Pattyn.

Starting with the mid-1980s, two new groups were gradually formed from the old one: one group around I. Dézsi, with a main interest in materials science, and another group around D.L. Nagy, with a main interest in solid-state physics. Although these groups have been sharing the same laboratories since then and are intensively cooperating in the methodology, the development of their research activity became rather independent.

The interest of the members of the materials science group turned to the study of the fundamental physical processes of ion implantation, the formation of various transitional metal silicides, and the investigation of the formation and structure of very thin layers.

For comparison of the phases formed after ion implantation of Te in Si and Ge to the amorphous systems, amorphous SixTe(1-x), GexTe(1-x), and single crystalline tellurides were studied. Ion implantation made it possible to incorporate atoms into target substrates in which the solubility of iron is extremely low. By measuring the isomer shift values in lattice sites, it was possible to present a new systematic of isomer shift of 57Fe in elements and pointed out the effects of d-d hybridization on the atomic charge density [5].

The ion-implantation studies were extended to metals and insulators, in the latter case to α-Al2O3, α-Fe2O3 [6], and to LiNbO3. In order to identify the annealing products in these target substrates, detailed studies were performed on spinels containing Co and Fe. A series of studies were performed on the formation processes of epitaxial CoSi2 on Si and SixGe(1-x) with the participation of A. Vantomme, G. Petô, and other collaborators. It was possible to successfully grow epitaxial CoSi2 layers of excellent quality on the surface of these substrates. Ternary silicide phases were also investigated [7]. It is worthwhile to mention here that we grew successfully 57Co doped β-FeSi2 crystals in a special furnace of gradual temperature and proved that the Co atoms populate both the two different crystal sites in the orthorhombic β-FeSi2.

Very thin (0.15–10 ML) 57Fe on Ag surfaces were grown in MBE in Leuven and investigated by using STM and Conversion Electron Mössbauer Spectroscopy. It was found that Fe deposits in clusters on the Ag single crystal surfaces and gradually the clusters cover the surfaces up to 10 ML thickness. The layers are paramagnetic up to 5 ML. For 57Co deposition, electroplating was applied. Very similar behavior to Fe was observed, but the sensitivity of the measurement increased significantly because of the radioactive tracing effect and by using a special resonance counter. The latter measurement was performed first by our group. The Mössbauer studies at low temperature are in progress.

Presently, the materials science group performs measurements on very low nanosized metal oxides, e.g., magnetite.

The main interest of the solid-state physics group in the 1980s was a topic stemming from cooperation with H. Spiering (Universität Erlangen and Universität Mainz before and after 1978, respectively) – the interpretation of the hyperfine interaction of high-spin Fe2+ ions in terms of ligand field theory utilizing Mössbauer measurements performed at low temperature in external magnetic field. In the 1970s, this method was successfully applied to a series of crystalline hydrates containing the Fe2+(H2O)6 coordination ion. A study of Fe(ClO4)2 frozen solution showed that, even in the amorphous environment, the same normal distortions, i.e., the bond-bending ones, are present as in the crystalline hydrates and also the local symmetry around the Fe2+ ion is the same [8].

A new kind of after-effect of the electron capture of 57Co – long-lived low-energy electronic excitations of nucleogenic high-spin Fe3+ – was found in cooperation with G. Ritter’s group (Erlangen) in various systems, including 57Co:LiNbO3. The effect made it possible to investigate for the first time the ligand field in short-lived excited terms of the nucleogenic ion [9]. More recently, a systematic study of the nucleogenic valence states lead to revisiting the model of competing acceptors [10].

L. Bottyán joined the solid-state physics group in 1986. With the appearance of the high-TC superconductors, he initiated Mössbauer studies on YBa2Cu3O7 and related systems. Probably the first Mössbauer emission study on a high-TC superconductor (57Co:YBa2Cu3O7) was done by the group. A scheme of the valance state of Fe and its coordination in YBa2Cu3O7-y was established [11].

Starting in 1992, the interest of the solid-state physics group gradually shifted to thin film magnetism as investigated with grazing-incidence nuclear resonant scattering of synchrotron radiation, a method that we prefer calling "Synchrotron Mössbauer Reflectometry" (SMR). The key phenomenon of this method is the so-called "total reflection peak" first predicted by L. Deák in 1994. A general anisotropic optical theory of SMR was developed 1996 in cooperation with H. Spiering (Universität Mainz) [12]. More recently, we demonstrated that the same formalism can be used for polarized neutron reflectometry (PNR) [13]. Since then, we successfully applied SMR to nanometer-resolution phase analysis of iron oxide films, to identifying finite-size effects in the magnetic structure of coupled multilayers, to demonstrating the bulk-spin-flop phenomenon in a coupled superlattice, etc.

Recently, SMR has been extended to off-specular scattering, thereby allowing for the study of antiferromagnetic domains in coupled multilayers. A new kind of domain transformation, the spin-flop-induced coarsening, has been discovered in a wide international cooperation by off-specular SMR and confirmed by PNR [14].

Structural and magnetic properties of molecular magnets were studied in the late 1990s by a cooperation of L. Bottyán with the Institute for Chemical Physics in Chernogolovka. Low-temperature high-field Mössbauer studies made possible, among other techniques, the interpretation of the negative magnetization in terms of the giant magnetocrystalline anisotropy in a 2D molecular ferrimagnet.

Considerable efforts have been invested into developing data reduction codes. SIRIUS, the standard fitting program of the group, stems in its original form from the late 1960s and the early 1970s. This program was the first realization of the "transformation matrix concept" of L. Pócs and is now widely used in many other Mössbauer codes. The first application of SIRIUS was the evaluation of lunar samples in 1971. Several mainframe versions of SIRIUS were used in the 1970s-1980s all over the world. In the late 1980s, a PC-DOS version of SIRIUS became the standard tool of many Mössbauer laboratories. Recently, we have been very much involved in developing the general simultaneous fitting environment EFFI of H. Spiering, Universität Mainz.

As for our teaching activity, we offer laboratory classes for undergraduate students. Diploma and Ph.D. students are often part of our groups. Two courses on nuclear solid-state physics are held at the Eötvös Loránd University (D.L. Nagy is affiliated part-time with the Department of Atomic Physics of the University).

The main technological background of both groups has been, since 1963, the laboratory of chemical technology and nuclear chemistry lead by B. Molnár. Besides standard chemical facilities, the laboratory is equipped with various vacuum furnaces, evaporation and electrolysis facilities, and all allowing handling of radioactive materials. Beginning at October 2003, molecular beam epitaxy (MBE) equipment will become operational.

Our groups are presently comprised of 13 people, some of them doing Mössbauer spectroscopy on a part-time basis only. These are (in the order of the cover photo, from the left to the right): L. Bottyán, M. Major, I.S. Szucs, I. Dézsi, B. Molnár, F. Tancziko, Zs. Kajcsos, D.L. Nagy, Cs. Fetzer, D. Merkel, L. Deák, E. Szilágyi, and J. Fenyves. Cs. Fetzer and I.S. Szucs are involved in materials science studies with I. Dézsi. Two Ph.D. students (M. Major and F. Tanczikó) as well as the diploma student D. Merkel are working on thin-film magnetism with L. Bottyán and D.L. Nagy. L. Deák is developing the theory of SMR and related methods. E. Szilágyi is mainly doing ion-beam analysis and, in part time, thin-film magnetism with SMR. Zs. Kajcsos’ primary method is positron annihilation, but he is also involved, in cooperation with K. Lázár (Institute of Isotope and Surface Chemistry), in Mössbauer studies on highly porous systems. In the 1980s, in Jülich and in Mainz, Zs. Kajcsos had significant contributions to Mössbauer spectroscopy, including time-differential emission Mössbauer spectroscopy and the investigation of surface magnetism with the depth-selective conversion electron Mössbauer spectroscopy (DCEMS). B. Molnár is running the laboratory of chemical technology and nuclear chemistry. Finally, J. Fenyves is technically assisting both research groups.

References

  1. I. Dézsi, L. Keszthelyi, "The observation of the Mössbauer Effect of 159Tb." In Proceedings of the Conference on the Mössbauer Effect in Dubna, 64/17-1 (1962).
  2. I. Dézsi, L. Keszthelyi, L. Pócs, L. Korecz, "Mössbauer Effect on Some Iron Salts in Ice." Phys. Lett. 14, 14 (1965).
  3. I. Dézsi, B. Molnár, T. Tarnóczy, K. Tompa, "On the Magnetic Behaviour of Iron (II)-bis-(1,10 Phenantroline) - Thiocynate between -190° and 30°." J. Inorg. and Nucl. Chem. 29, 2486 (1967).
  4. I. Dézsi. Proc. Conf. Appl. Mössbauer Effect, Tihany, 1969. Akadémiai Kiadó, Budapest (1971).
  5. I. Dézsi, U. Gonser, and G. Langouche, "Systematics of the Isomer Shifts of 57Fe in various Hosts." Phys. Rev. Lett. 62, 1659 (1989).
  6. I. Dézsi, I. Szucs, Cs. Fetzer, H. Pattyn, G. Langouche, H.-D. Phannes, R. Magalhães-Paniago. "Local interactions of 57Fe after electron capture of 57Co implanted in α-Al2O3 and in α-Fe2O3." J. Phys.: Cond. Matter 12, 2291-2296 (2000).
  7. Cs. Fetzer, I. Dézsi, A. Vantomme, M. F. Wu, S. Jin, H. Bender. "Ternary CoxFe(1-x)Si2 and NixFe(1-x)Si2 formed by ion implantation in silicon." J. Appl. Phys. 92, 3688 (2002).
  8. H. Domes, O. Leupold, D.L. Nagy, G. Ritter, H. Spiering, B. Molnár, I.S. Szucs. "Mössbauer study of short range order in frozen aqueous solutions of Fe(ClO4)2." J. Chem. Phys. 85, 7294 (1986).
  9. R. Doerfler, W. Gruber, P. Gütlich, K.M. Hasselbach, O. Leupold, B. Molnár, D.L. Nagy, G. Ritter, H. Spiering, F. Tuczek. "Mössbauer spectroscopic evidence of angle-dependent inter-system crossing in LiNbO3:Fe3+." Phys. Rev. Lett. 57, 2849 (1986).
  10. T. Becze-Deák, L. Bottyán, G. Corradi, L. Korecz, D.L. Nagy, K. Polgár, S. Sayed, H. Spiering. "Electron trapping centres and cross sections in LiNbO3 studied by 57Co Mössbauer emission spectroscopy." J. Phys.: Cond. Matter 11, 6239 (1999).
  11. L. Bottyan, B. Molnar, D.L. Nagy, I.S. Szucs, J. Toth, J. Dengler, G. Ritter, J. Schober. "Evidence for Fe4+ in YBa2(Cu1-xMx)3O7-y (M=57Co,57Fe) by absorption and emission Mössbauer spectroscopy." Phys. Rev. B 38, 11373 (1988).
  12. L. Deák, L. Bottyán, D.L. Nagy, H. Spiering. "The coherent forward scattering amplitude in transmission and grazing incidence Mössbauer spectroscopy." Phys. Rev. B 53, 6158 (1996).
  13. L. Deák, L. Bottyán, D.L. Nagy, H. Spiering. "A common optical algorithm for the evaluation of specular spin polarized neutron and Mössbauer reflectivities." Physica B 297, 113 (2001).
  14. D.L. Nagy, L. Bottyán, B. Croonenborghs, L. Deák, B. Degroote, J. Dekoster, H.J. Lauter, V. Lauter-Pasyuk, O. Leupold, M. Major, J. Meersschaut, O. Nikonov, A. Petrenko, R. Rüffer, H. Spiering, E. Szilágyi. "Coarsening of Antiferromagnetic Domains in Multilayers: The Key Role of Magnetocrystalline Anisotropy." Phys. Rev. Lett. 88, 157202 (2002).

Mössbauer Laboratory at the Institute of Isotope and Surface Chemistry
Chemical Research Centre
Hungarian Academy of Sciences
Budapest

Károly Lázár
Institute of Isotope and Surface Chemistry
Chemical Research Centre
Hungarian Academy of Sciences
Budapest

From Left to Right: Károly Lázár, Annamária Murányi-Szeleczky, János Megyeri, and László Szirtes.

The Mössbauer Laboratory at the Institute of Isotope and Surface Chemistry was established in 1979 as a part of the Catalysis Department (headed at that time by László Guczi). The Department of Catalysis and Tracer Studies was formed in 1992, and the Laboratory is one of the constituting groups of that Department since that time.

The main activity of the Laboratory is studying catalysts by in-situ Mössbauer spectroscopy. Mostly the conventional measuring technique, transmission 57Fe spectroscopy, is applied. During the early period, iron-base Fischer-Tropsch catalysts were studied. Then a slightly broader field – bimetallic supported catalysts (Fe-Ru, Fe-Pd) for CO + H2 conversion reactions – were investigated. These catalysts were prepared by decomposing bimetallic carbonyls. In a short series, amorphous quenched metal catalysts were also studied. From the 1990s, the study of various zeolitic systems commenced as well. As one possibility – utilizing the spatial confinement provided inside the zeolite cages - small metallic particles can be formed. In this field, successful preparation of PdFe nanoparticles was achieved in Y zeolite. In another preparation method, metallic iron was formed in the cages of Y zeolite by reduction of iron ions with sodium-azide. The other aspect originates from the strictly determined structure of zeolites. The symmetries are determined; thus, iron sites can be identified. In this way steps of solid-state ion exchange were monitored (e.g., in the process of FeCl2 + NH4-Zeol → Fe-Zeol + NH3 ↑ + HCl ↑.) Furthermore, a variety of isomorphously substituted Fe zeolites (BEA, FER, MFI, MWW, TON) have also been studied. The framework and extra-framework types of iron can be distinguished by evacuation or by studying their reducubility. Presence of dinuclear Feframework-O- Feextra-framework species is also suggested from their respective spectra. 119mSn measurements have also been carried out, on Pt-Sn/SiO2 and PtSn/Al2O3 systems – the formation of various PtxSny alloys was monitored – and on stannisilicate zeolite analogs (MFI, MEL, MTW). Recently, mesoporous systems (MCM-41 and SBA-15) are studied both by 57Fe and 119mSn spectroscopies. Coordination and states of iron and tin are distinctly different in comparison to those found in zeolites under similar conditions.

Approximately 80 papers have been published based, at least in part, on the work performed in the Mössbauer Laboratory. A more detailed description can be found on the Laboratory’s home page: <www.iki.kfki.hu/catrace/Mosba.html>. The staff at present consists of Károly Lázár (head) and research fellows János Megyeri, Annamária Murányi-Szeleczky (part-time), and László Szirtes (part-time). Several students have also contributed to the work of the Laboratory, by performing measurements for Ph.D. or MS theses.

In the near future, we would like to construct an in-beam Mössbauer facility in which the generation and excitation of the Mössbauer source nuclei would be provided by continuous irradiation with neutrons. The project has already commenced in cooperation with the Department of Nuclear Research – the respective beam line at the Budapest Neutron Centre is under development.


Department of Nuclear Chemistry
Eötvös Loránd University
Budapest

Zoltán Homonnay and Attila Vértes
Department of Nuclear Chemistry
Eötvös Loránd University
Budapest

Upper Row From Left to Right: Sándor Nagy, Attila Vértes, Zoltán Homonnay, Erno Kuzmann, Zoltán Klencsár, Zoltán Németh (Ph.D. student), and Sándor Stichleutner (Ph.D. student).
Front Row From Left to Right: Helga Sz. Tunyogi (Secretary), Szilvia Kárpáti (Undergraduate), Petra Á. Szilágyi (Undergraduate), and Krisztina Kovács (Undergraduate). (The last three, although undergraduates, are very serious Mössbauer spectroscopists!)

The first Mössbauer spectrometer was put into operation at the Department of Physical Chemistry and Radiology in the Institute of Chemistry of Eötvös Loránd University in 1967. This device was a Hungarian-made spectrometer, designed and built with the help of an electrical engineer János Soós, as well as that of Lajos Keszthelyi and István Dézsi who worked at the Central Research Institute for Physics (KFKI) and had already achieved substantial experience in the application of the Mössbauer effect by that time.

The subject of the first measurements carried out together with István Dézsi was Mössbauer analysis of the corrosion products of iron. The results were published in 1967, first in Hungarian with an English version released in 1969 [1]. This was the first paper that showed that Mössbauer spectroscopy is a unique tool to study the corrosion of iron.

Mössbauer investigation of frozen solutions began in the mid-1960s by Lajos Keszthelyi and István Dézsi. The special experimental quenching technique developed by them was used later by Attila Vértes in order to explore the chemical structure of solutions [2].

The mean time of the paramagnetic spin relaxation (τ) could be raised by applying dilute (< 0,05 M) iron(III) solutions at low temperature (< 80 K) so that magnetic hyperfine splitting showed up in the Mössbauer spectra. From the measured value of the magnetic hyperfine field, the chemical effect of the ligands on the central Fe3+ ion could also be deduced [3]. Dimerization of Fe3+ species in the solution was shown by the observation of magnetic to paramagnetic transition (due to accelerated spin-spin relaxation) [4]. If polymerization or coalescence of Fe3+ species occurs in the solution, the size distribution of the resultant superparamagnetic particles can be determined from the temperature dependence of the Mössbauer spectra [5].

Our group showed first that the Mössbauer effect can occur in the liquid phase at room temperature in the microporous "thirsty glass" (micropore diameter ~4 nm) [6].

A respected cooperation partner of the group in the application of Mössbauer spectroscopy on solution and coordination chemistry was Kálmán Burger, professor of the University of Szeged, who died in 2000.

The group, in cooperation with researchers of Lehigh University, Bethlehem, PA (Professors Leidheiser and Simmons), did pioneering work in the application of Mössbauer spectroscopy in electrochemistry, publishing dozens of papers in the field.

More recent activity of the group included Mössbauer studies of aluminum alloys, electrodeposits, amorphous systems, superconductors, and colossal magnetoresistant materials [7-12]. In addition to these fields, the group is active in numerous other applications (e.g., minerals, coordination chemistry).

The group loosened its ties with the Department of Physical Chemistry and Radiology in 1983 when the Laboratory of Nuclear Chemistry was established, which in a few years was declared as the Department of Nuclear Chemistry headed by Prof. Attila Vértes. (The Department’s other important research activity is positron annihilation spectroscopy.)

In the mid-1990s, the Research Group for the Application of Nuclear Methods in Structural Chemistry headed by Prof. Attila Vértes was created. This Research Group is sponsored by the Hungarian Academy of Sciences. In 1999, Prof. Vértes resigned as Department Head due to age limitation rules. His follower is Prof. Zoltán Homonnay, former student of Prof. Vértes. Thus the Mössbauer "crew" at the Chemistry Institute of Eötvös University is now composed of colleagues affiliated to the Department (Zoltán Homonnay, Professor, Head; Sándor Nagy, Associate Professor; Attila Vértes, Professor; and Zoltán Németh, Ph.D. student) and to the Research Group of the Hungarian Academy of Sciences (Attila Vértes, Head; Ernô Kuzmann, Research Professor; Zoltán Klencsár, Research Associate Professor). Former member of the Department Ilona Nagyné-Czakó retired in 1995. György Vankó, former member of the Research Group, left in 2001. About 40 Masters and 30 Ph.D. students prepared their theses in our Laboratory in the past two to three decades.

The Department of Nuclear Chemistry has the privilege of offering Nuclear Chemistry as an obligatory course to all chemistry major students. Since Mössbauer spectroscopy is part of this course, there is a large pool from which to select future Mössbauer spectroscopists. Currently, two Ph.D. students, two Masters (finishing their diploma), three 4th-year students (starting their diploma work next year), and another 3rd-year student (doing undergraduate research) are directly involved in Mössbauer research in various fields. The Department and the Research Group currently have seven Mössbauer spectrometers, all in constant operation, normally with three to four 57Co, one to two 119mSn, and one 151Eu sources available.

Three monographs and several book chapters dealing with Mössbauer spectroscopy were published by our group.

There is hope that the application of Mössbauer spectroscopy will continue for a long time in the Chemistry Institute of Eötvös University, Budapest.

References

  1. I. Dézsi, A. Vértes, L. Kiss, "Mössbauer study of the corrosion products of iron." Magyar Kémiai Folyóirat 73, 412 (1967); J. Radioanal. Chem. 2, 183 (1969).
  2. A. Vértes, S. Nagy, I. Nagy-Czakó, É. Csákvári, "Mössbauer study of equilibrium constants of solvates. I. Determination of equilibrium constants of tetraiodotin-trimethyl-isopropoxylane and tetrabromotin-acetic anhydride solvates." J. Phys. Chem. 79, 149 (1975) and A. Vértes, I. Nagy-Czakó, K. Burger, "Mössbauer study of equilibrium constants of solvates. 2. Determination of some solvation parameters of tin tetrahalides." J. Phys. Chem. 80, 1314 (1976).
  3. A. Vértes, F. Parak, "A study of the relationship between the spin relaxation and certain chemical properties of paramagnetic iron(III)-salt solutions by Mössbauer spectroscopy." J. Chem. Soc. Dalton Trans., 2062 (1972).
  4. A. Vértes, I. Nagy-Czakó, K. Burger, "Mössbauer study of equilibrium constants of solvates. Solvent-solute interactions in non-aqueous solutions of iron(III) chloride." J. Phys. Chem. 82, 1469 (1978).
  5. A. Vértes, L. Korecz, K. Burger. Mössbauer-spectroscopy. Elsevier: Lausanne (1979), pp. 331-334.
  6. K. Burger, A. Vértes, "Capillary Mössbauer spectroscopy for solution chemistry." Nature 306, 353 (1983).
  7. L. Murgás, Z. Homonnay, S. Nagy, and A. Vértes, "Investigation of Phase Transformation in an Al-0.58 Wt Pct Alloy by Mössbauer Spectroscopy." Metallurgical Transactions 19A, 259-264 (1988).
  8. E. Kuzmann, Z. Homonnay, A. Vértes, M. Gál, K. Torkos, B. Csákvári, K. Sólymos, G. Horváth, J. Bánkuti, I. Kirschner, and L. Korecz, "Metastability in EuBa2(Cu1-xSnx)3O7-y Studied by 119Sn and 151Eu Mössbauer Spectroscopy." Phys. Rev. B 39, 328-333 (1989).
  9. Gy. Vankó, Z. Homonnay, S. Nagy, A. Vértes, G. Pál-Borbély, H.K. Beyer, "On the synthesis and steric distortion of the tris(2,2'-bipyridine)iron(II) complex ion in zeolite-Y." JCS Chemical Communications, 785-786 (1996).
  10. Z. Homonnay, Z. Klencsár, V. Chechersky, Gy. Vankó, M. Gál, E. Kuzmann, S. Tyagi, J.-L. Peng, R.L. Greene, A. Vértes and A. Nath, "The effect of praseodymium on the lattice dynamics and electronic structure of the Cu(1)-O(4) chain in Y1-xPrxBa2Cu3O7-δ. Phys. Rev. B 59, 11596-11604 (1999).
  11. Z. Homonnay, K. Nomura, G. Juhász, M.Gál, K. Sólymos, S. Hamakawa, T. Hayakawa, and A. Vértes, "Simultaneous probing of the Fe- and Co-sites in the CO2-absorber perovskite Sr0.95Ca0.05Co0.5Fe0.5O3-δ: a Mössbauer study." Chemistry of Materials 14, 1127-1135 (2002).
  12. Z. Klencsár, E. Kuzmann, Z. Homonnay, A. Vértes, A. Simopoulos, E. Devlin, G. Kallias, "Interplay between magnetic order and the vibrational state of Fe in FeCr2S4." Journal of Physics and Chemistry of Solids 64, 325.

Research Institute for Solid-State Physics
Hungarian Academy of Sciences
Budapest

Imre Vincze
Research Institute for Solid-State Physics
Hungarian Academy of Sciences
Budapest

From Left to Right: Dénes Kaptás, Senior Scientist; László Bujdosó (back), Engineer; Tamás Kemény, Scientific Advisor; Imre Vincze (back), Scientific Advisor; Judith Balogh, Senior Scientist; György Pesti, Technician; Gyula Faigel, Research Professor, Corresponding Member of the Hungarian Academy of Sciences; Miklós Tegze, Scientific Advisor; Gábor Bortel, Senior Scientist.

Our Non-Equilibrium Alloys research group is a branch of the Mössbauer group founded by L. Keszthelyi. Technical improvements made by L. Keszthelyi, I. Dézsi, L. Cser, and the engineering corps of the Central Research Institute for Physics, Budapest (KFKI), resulted in high-quality equipment around 1970. This equipment was suitable for studying the subtle alloying effects of iron, which manifested mainly in changes of the line shape. Until about 1974, the temperature and composition dependent studies of the impurity effects in iron were our main research objects, and they were performed in close cooperation with I.A. Campbell (Orsay). Information on the conduction electron polarization contribution of the iron hyperfine field and on the anomalous temperature dependence of certain impurity magnetic moments (Mn, Ru, Os, Ni, Pd, Pt) was obtained. Later, correlations between the iron hyperfine fields and the magnetic moments in concentrated binary, pseudo-binary alloys and intermetallic compounds were studied together with A.J. Meyer’s group in Strasbourg. Thanks to the invitation of I. Vincze by M.G. Kalvius (1975-76), a collaboration with F.E. Wagner in Munich was also established. The research on metallic glasses started shortly after the discovery of this new family of materials, and an important result in this field – the similarity of the short-range order of amorphous alloys and certain intermetallic compounds – was achieved in works performed in Budapest and in Groningen (1979-87) together with the group of F. van der Woude. In the early 1990s, the effect of large external magnetic field on the spinglass-like behavior in amorphous Fe-Zr and related alloys was investigated.

Recent research programs aim to study different nanostructured materials prepared by ball milling (e.g., Fe, Fe-B, Fe-Al), magnetic multilayers (e.g., Fe-B, Fe-Ag) evaporated in high vacuum, and nanocrystallized amorphous ribbons (e.g., Fe-Zr-B-Cu and related alloys). In a comparative study of these systems, it was found that nonequilibrium alloying in nanostructures play an overwhelming role in the deviation of the hyperfine fields from the bulk value and the grain boundary effects cannot be separated. Nonequilibrium mixing in nanostructures takes place even in cases when the elements are unsolvable in the bulk state (e.g., Fe-Ag). With diminishing grain size, superparamagnetic relaxation of the grains becomes dominant. In the case of soft magnetic nanocrystalline alloys, this may result in magnetic decoupling of the bcc grains from the ferromagnetic residual amorphous matrix. At present, investigations on the external magnetic field dependence of the superparamagnetic relaxation of nanometer size particles and the possibility of field induced collective behavior in concentrated small particle system is in progress.

Another line of Mössbauer effect-related research started at the end of the 1980s. Experiments based on the resonant scattering of Mössbauer quanta were initiated by G. Faigel. These included various measurements using laboratory and synchrotron sources: The possibility of laboratory source-based diffraction experiments on powdered samples was demonstrated. A monochromator was made for the 151Eu resonance and the technique of the nuclear resonant scattering of synchrotron radiation was extended to this isotope. Quantum beats on Eu2O3 and EuS powder mixture were measured. Theoretical works on inside source gamma holography based on the interference of recoil free scattered photons were done. The setting up of an experimental station for gamma holography is underway.


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