Reprinted from the November 2003 edition of the Mössbauer Spectroscopy Newsletter, published as part of Volume 26, Issue 9 of the Mössbauer Effect Reference and Data Journal

Mössbauer Spectroscopy in Israel

Professor R. H. Herber
Condensed Matter Physics Group
Racah Institute of Physics
The Hebrew University of Jerusalem
91904 Jerusalem

L-R: Israel Nowik, Erika Bauminger, Rolfe Herber, and Israel Felner

Work on the Mössbauer effect in Jerusalem started soon after Professor Mössbauer's paper was published in 1958 and continues vigorously today. The very first to introduce the Mössbauer effect in this laboratory were S. Cohen and S. Ofer, who were soon joined by E. R. Bauminger and I. Nowik. I. Felner joined the group in 1972. Over the years many graduate students have been involved in the experiments.

The first of these were performed with very primitive equipment – using a mechanical drive, whose velocity was changed in steps, and data were collected manually during 24 hours, with all involved taking turns through night shifts. The first papers published by the group in 1960 dealt with the Fe Mössbauer effect in garnets and magnetite, but later the group was involved mainly with the Mössbauer effect in the rare earth region. These studies started with the discovery of the Mössbauer effect in ¹⁶¹Dy, and opened a wide field of research in the physics of lanthanide compounds. Included were studies of magnetically ordered systems (garnets and intermetallic compounds), spin relaxation in paramagnetic systems, anisotropic lattice dynamics, and the discovery of large temperature dependent isomer shifts in europium intermetallics, associated with fast valence fluctuations between different 4f configurations. In the 1970s research also included studies of actinide compounds, using several Mössbauer isotopes, in particular ²³⁷Np (together with J. Gal, Nuclear Research Center Negev, Beer Sheva, Israel). In later years the studies dealt mainly with studies of various magnetic phenomena, applying the Mössbauer effect in ⁵⁷Fe and ¹⁵¹Eu together with magnetic measurements, and the application of the Mössbauer effect in iron to biological and medical problems. The group suffered a serious loss with the deaths of S. Ofer and S. Cohen in 1983-1984. In 1995, R. Herber joined the group, after 35 years on the faculty of Rutgers University in the United States, where he headed the Mössbauer group from 1959. The group today consists of Professors Bauminger, Felner, Herber, and Nowik.

Application to Biological and Medical Problems: In recent years, the research in this area has concentrated mainly on:

(a) Protein dynamics.

(b) The function of iron in various diseases, as e.g. in thalassemia (with E. Rahmilewitz from the Hadassa Hospital in Jerusalem), in malaria (with H. Ginsburg and G. Blauer from the Biochemistry Department at The Hebrew Unversity), and recently in Parkinson’s disease (with J. Galazka Friedman from Warsaw Technical University and A. Friedman from Warsaw Medical University).

(c) Initial stages of iron accumulation in mammalian and bacterial ferritins and structure-function relations in these proteins (with the group of P. Harrison from the Biochemistry Department at Sheffield University, U.K.).

Organometallics and Inorganic Compounds: Among the major research interests of our group are the determination and elucidation of metal atom hyperfine interactions and dynamics by carrying out temperature-dependent Mössbauer effect studies over the range 4.2 to 400 K. Much of this work is made possible by collaborating with other groups who specialize in the synthesis of appropriate subject compounds, and such collaborations have proven to be exceptionally fruitful in facilitating the study of a variety of organometallic and inorganic complexes:

(a) Ferrocene and ferrocenoid organometallics:

(i) The Gol’danskii-Karyagin Effect (GKE) in ferrocene and its relation to bonding anisotropy (with H. Schottenberger, University of Innsbruck).

(ii) The GKE in cyclopentadienyl-Fe-H₄ and related compounds.

(iii) C₆₀ ferrocenoids and C₆₀ ferrocenoid sandwich compounds (with E. Nakamura, University of Tokyo).

(b) Octamethyl ferrocene and related organometallics:

(i) Rotator molecules and the f anomaly.

(ii) ⁵⁷Fe labeled materials and spin-lattice relaxation (with H. Schottenberger, University of Innsbruck).

(iii) High pressure effects on the f anomaly in rotator molecules (with S. Nasu, Osaka University).

(c) Organometallics with η⁵-P rings and related molecules:

(i) Mixed sandwich compounds.

(ii) Spin-lattice relaxation in one-electron oxidation products (with A. Kudinov and A. N. Nesmeyanov, Institute of Organo-Element Compounds, Moscow).

(d) BO and B(CH₃)₂ ring ferrocenoids (with M. Wagner, University of Frankfurt).

(e) Organotin(II) compounds:

(i) Stannylium cation and GKE effect (with J. B. Lambert, Northwestern University).

(ii) Organotin(II) analogues of acetylene (with P. P. Power, University of California Davis).

Magnetism and Superconductivity: The group continues the extensive research of magnetic and superconducting materials, using the ¹⁵¹Eu, ⁵⁷Fe, and ¹¹⁹Sn isotopes. Some of the subjects of these studies in recent years include:

(a) ⁵⁷Fe and ¹¹⁹Sn hyperfine interactions in compounds which show coexistence of superconductivity and magnetism.

(b) ¹⁵¹Eu, and dilute ⁵⁷Fe and ¹¹⁹Sn studies of various rare earth and/or ruthenium oxides, CaRu_1-xM_xO₃, SrRuO₃, Sr₂FeRuO₃, EuRuO₃, Eu₂Ru₂O₇, EuSr₂Ru_1-xCu_xO₆.

(c) Various Ruddlesden-Popper phases (with M. Greenblatt, Rutgers University).

(d) Nanoparticles of iron compounds and alloys, sonochemically prepared (with A. Gedanken, Bar-Ilan University, Israel).

(e) Ferrites and iron garnets (with M. Ristic and S. Music, Ruder Boskovic Institute, Zagreb, Croatia).

(f) Ruthenates which show coexistence of superconductivity and weak-ferromagnetic order (which was first prepared and analyzed in our laboratory). The major problem in these materials is the magnetic structure of the Ru sublattice.

(g) Amorphous magnetic nanoparticles such as NiFe₂O₄, Fe₃O₄, Co, and Ba hexaferrites with particular attention to their hyperfine parameters (with A. Gedanken, Bar-Ilan University).

(h) Phase transformations in amorphous iron oxide magnetic nanoparticles, which arise during annealing in air or vacuum, as well as the magnetic properties of amorphous iron oxide coated with cobalt or by submicrospherical alumina. Investigation of the blocking temperatures of amorphous iron nanoparticles coated with various surfactants.

(i) The magnetic properties of iron-filled nanotubes and other magnetic nanorods and the particle size effects on the magnetic and hyperfine parameters of such systems.

Professor Moshe Paz Pasternak
School of Physics and Astronomy
Tel Aviv University
Ramat Aviv
IL-69978 Tel Aviv

The current members of the TAU Mössbauer group having their daily divine guidance from Dr. Albert Einstein (statue). L-R: Noaz, Weiming, Moshe, and Ella.

The Tel Aviv University (TAU) Mössbauer group started its activity in the early 1970s. The main studies were focused on matrix-isolation methodology using ⁵⁷Fe and ¹¹⁹Sn in solid rare and reactive gases. The switching point in its research interest can be traced to the Leuven ICAME conference, where two papers were concurrently presented (Hyperfine Interactions 33, 1985): "⁵⁷Co implanted in reactive and non-reactive frozen gases" and "Mössbauer spectroscopy in iodine at pressure to 30 GPa." This event symbolized the crossover phase transition, from negative to positive pressure Mössbauer spectroscopy activities, into a new era of exciting breakthroughs and new discoveries in high pressure state of matter using ¹²⁹I and ¹¹⁹Sn Mössbauer spectroscopy combined with diamond anvil cells (DACs).

A second major development took place in the early 1990s. It followed our discovery of the Mott-Hubbard d-d correlation breakdown in the antiferromagnetic Ni 129I 2 applying Mössbauer spectroscopy, resistivity, and x-ray diffraction (XRD) measurements ( PRL 65, 1990). It was then decided to switch our activity entirely to high-pressure studies combining resistivity, XRD, and 57Fe into the 100 GPa range (100 GPa = 1 Mbar ~1 eV/Å3) [1]. But for such pressures one needs absorbers in the 100 – 50 µm diameter scale! At that time no suitable DACs, appropriate diamond anvils, and intense, albeit miniature, 57Co sources were commercially available [2].

The point-source DAC setup and a demonstration of the miniscule absorber, contrasted with 0.15 mm tungsten wire.

A perforated anvil with a miniature 0.5 mm height anvil on top.

Finally all those experimental goals were achieved: opposing-plates (P <80 GPa) and piston-cylinder miniature DACs were developed and built ( RSI 60, 1990; 69, 1998) allowing for short source-absorber distances (~1.5 mm), pressures far beyond 100 GPa, and cryogenic temperatures and heating up to 300° C. Close cooperation with a Moscow-based company led to the development of a 10 mCi high specific activity 57Co(Rh) "point" source (0.5 x 0.5 mm). Only recently, a technical breakthrough took place at our lab with the development of perforated anvils ( RSI 72, 2001) allowing the trebling of the 14.4 keV transmission through the diamonds and substantially enhancing the 14.4 keV signal/BG.

The TAU Mössbauer spectroscopy group personnel consist of Dr. Ella Milner, Dr. Weiming Xu, Dr. Moshe P. Pasternak, one graduate student, and a technician. I should mention Dr. R. Dean Taylor of Los Alamos National Laboratory, USA, who has been collaborating with us for many years. The Mössbauer activity is part of a larger TAU High Pressure group operation carrying transport studies, XRD (at ESRF), and development of new DACs and anvils. The Mössbauer group uses three LHe cryostats, furnaces, and a small chemistry lab for synthesis of material with enriched 57Fe isotopes. Our Mössbauer spectroscopy studies led to several important discoveries, including pressure-induced (PI) high to low-spin transitions and breakdown of magnetism (Mott-Hubbard transition) in ferric and ferrous ionic compounds ( PRL 79, 1997; 82, 1999), PI amorphization of FePO 4 ( PRL 79, 1997), PI coordination crossover in magnetite ( JMMM 265, 2003), PI self-oxidation of Fe 2+(OH) 2 ( PRL, to be published), and many others. The group has strong ties with international physics and geophysics groups and labs. Its members often appears as invited speakers in prestigious international scientific meetings, conveying the message regarding the uniqueness of Mössbauer spectroscopy in unraveling properties of magnetism and structure, on the atomic scale, at very high density of matter.

The development of a diamagnetic hematite with pressure increase.

[1] The need for such high pressures were foreseen due the large correlation gap, ~eVs, present in antiferromagnetic iron insulators.

[2] It should be mentioned that at that time HP-DAC ⁵⁷Fe studies were being carried out in Japan, using conventional ⁵⁷Co(Rh) sources and DACs which limited pressure to <100 GPa, ambient temperature measurements, and extremely lengthy recording time (~1 week or more for a spectrum).