Biographical Sketch of W. Keune
Reprinted from the September 2006 edition of the Mössbauer Spectroscopy Newsletter, published as part of Volume 29, Issue 7 of the Mössbauer Effect Reference and Data Journal

Professor Doctor Werner Keune of the University of Duisburg-Essen has spent more than 38 years (nearly four decades!) of his academic life focusing on the various applications of Mössbauer spectroscopy. Professor Keune (known simply as Werner in our community) officially retired in January 2006, but continues to be a very active Mossbauer researcher. Over the last four decades Werner has been the author/co-author of almost 200 research papers, with scientific collaborations from a very large number of countries, including Brazil, the US, Italy, India, Japan, Russia, Romania, and Spain. He has made significant contributions to the applications of this technique in specialized areas, such as thin films, surfaces and interfaces, and multilayers, and is considered to be a world-class Mössbauer researcher and an esteemed physicist.

Werner Keune was born on 11 June 1939 in Saarbrücken, Germany. After the Second World War, his parents, Dora and Kurt Keune (his farther was a mining engineer with a strong background in natural sciences) moved to several places in Germany. Werner grew up in Southern Germany in a small town near the city of Heilbronn, where the great natural scientist and physician Julius Robert von Mayer proposed the first law of thermodynamics in 1842. Werner graduated from high school in 1958 and, influenced by the book “The Evolution of Physics” by Albert Einstein and Leopold Infeld, he decided to become a physicist. He graduated with a diploma in physics from the Institute of Technology (now Technical University) in Munich in 1965. In his diploma thesis he investigated the optical absorption of radiation-induced defects in quartz under the supervision of Professors Heinz Maier-Leibnitz and Werner Schmatz. In 1966, he decided to continue his education for his Ph.D. degree in a very challenging area, namely optical and Mössbauer effect investigations of matrix-isolated Fe impurities in solid neon, under the supervision of Professor Edgar Lüscher. He had to build a vacuum system for rare-gas matrix isolation, including Knudsen cells for controlled 57Fe evaporation, and since then he has developed an enthusiasm for vacuum deposition of thin films. (In those days, commercial set-ups were not easily available and, of course, were costly as well.) In the same laboratory in Munich, Werner worked side-by-side with Hans Micklitz, who also used nuclear methods to study rare-gas matrix isolated atoms.

Because the isotope 57Fe was too expensive for the Munich laboratory, in 1967 Werner moved with his equipment to the famous North American Aviation Science Center in Thousand Oaks, California, USA, where Ulrich “Uli” Gonser was the leader of a cutting-edge Mössbauer group, including such Mössbauer pioneers as Ron W. Grant, Art H. Muir, Jr., and Robert M. Housley. Here at the Science Center, Werner was trained in Mössbauer spectroscopy and became a kind of “addicted researcher” to this method. He measured the hyperfine parameters of Fe and Fe oxide clusters in solid neon, and determined the absolute Lamb-Mössbauer factor of SnTe using 125Te.

Werner Keune as a graduate student in front of his rare-gas matrix isolation apparatus. Picture taken in the Science Center, Thousand Oaks, California, USA, in 1968.

The enthusiastic scientific atmosphere in Uli Gonser’s group shaped Werner’s attitude towards research for his whole life. Simultaneously, he enjoyed the American way of life and benefited from the hospitality of the Gonser family. He became a member of the Science Center hobby soccer team, with three Mössbauer spectroscopists in the crew.

The Science Center hobby soccer team, in 1968. Bottom row: Ulrich Gonser (first from right), Werner Keune (second from right). Middle row: Robert M. Housley (second from right).

In 1969, Werner returned to the Technical University of Munich and received his Ph.D. degree. Professor Rudolf L. Mössbauer was in his examination committee.

Also in 1969, almost simultaneously with Alfred “Ali” X. Trautwein, Werner Keune joined the newly established Mössbauer spectroscopy group of Professor Ulrich Gonser at the Institute of Metal Physics, University of Saarland, in Saarbrücken, Germany, and later became Assistant Professor and leader of the project “Mössbauer Spectroscopy Applied to Ferroelectrics” within the “Sonderforschungsbereich” (research network) on ferroelectrics. Werner is thankful to Uli Gonser for the inspiring atmosphere and scientific freedom found in his institute.


Werner and his wife Ingeborg during the ICAME 1999 in Garmisch, Germany.
In that year, in the foreign student club of the Saarbrücken campus, Werner met for the first time his later wife, Ingeborg Krummel, a high school teacher in biology and geography. At Saarbrücken, in collaboration with Istvan Dezsi (Budapest) and Sadgopal K. “Ashok” Date (the Alexander von Humboldt post-doc Fellow from India), Werner investigated photorefractive Fe centers, valency conversion, and spin relaxation effects in ferroelectric LiNbO3:57Fe.

Together with Saburo Nasu (Japan), Don L. Williamson (USA), and Teruya Shinjo (Japan), who all worked as post-docs at Saarbrücken, Werner applied Mössbauer spectroscopy to study Fe-Ni Invar alloys, fcc-Fe precipitation in CuFe alloys, and interface magnetism in nanoscaled ultrahigh-vacuum (UHV) grown Fe/Cu multilayers using the 57Fe probe-layer technique for the first time [1]. Also, antiferromagnetism of epitaxial fcc-Fe thin films embedded in Fe/Cu multilayers was discovered [2]. In 1972, Werner Keune worked in Brazil as “technical expert” of the IAEA (Vienna) in order to support the Mössbauer spectroscopy group of Alexandre Sette Camara in Belo Horizonte. Werner Keune received the degree of “Habilitation” at Saarbrücken in 1975, and in the same year moved to the Department of Physics, University of Duisburg (now University of Duisburg-Essen) in Duisburg, Germany, after accepting an invitation to join as Professor of Applied Physics.

At Duisburg, together with Joachim Lauer and Hans-Dieter Pfannes, Professor Keune had to build up a new Mössbauer spectroscopy laboratory from scratch. He focused his research on structural and magnetic properties of thin films and multilayers, including film preparation by molecular beam epitaxy (MBE). His group and Toshihiko Shigematsu, a post-doc at Duisburg, performed the first depth-selective conversion electron Mössbauer spectroscopy (DCEMS) experiment under clean UHV conditions [3].

Werner Keune and his group at Duisburg in 1999, with visiting scientists (top row) Hans-Dieter Pfannes, Brazil (first from right) and Masaaki Doi, Japan (fifth from right).

Later, Waldemar A. A. Macedo (Brazil), who then was a graduate student in Keune’s group, constructed and implemented an efficient UHV compatible electrostatic electron spectrometer for DCEMS, which allowed non-destructive depth-selective metallurgical phase analysis of ion-implanted surface layers. Professor Keune’s activities in DCEMS resulted in close and fruitful worldwide cooperation with Professor Kazuo Hisatake (Japan) and his coworkers at that time (Tamotsu Toriyama and Keiji Saneyoshi), David Liljequist (Sweden), Rudi H. Nussbaum (USA), Joan Parellada (Spain), Ognian Nikolov (Bulgaria), and Helfried Reuther (Germany). The non-destructive determination of the depth profile of buried semiconducting beta-FeSi2 layers by DCEMS in 57Fe ion-implanted silicon was a major achievement  [4,5]. Other important discoveries are related to the observation of a magnetic double transition in AuFe re-entrant spin glasses [6,7], thickness dependent ferro- or antiferromagnetism in epitaxial fcc-Fe(001) ultrathin films on Cu(001) in UHV [8,9], magneto-volume effects of gamma-Fe precipitates in Cu and CuAl matrices [10], and the site and isotope selective atomistic observation of a magnetic hysteresis loop in Tb/Fe multilayers with perpendicular magnetic anisotropy [11]. In cooperation with Fabienne Richomme and Professor Jacques Teillet (France) Werner Keune and his group investigated Tb/Fe multilayers by Mössbauer spectroscopy for many years. Werner Keune was group leader in the state-funded research networks (“Sonderforschungsbereich”) “Structural and Magnetic Phase Transitions in Transition Metal Alloys and Compounds” and “Magnetic Heterostructures” between groups of the Ruhr-Univerity Bochum and the University of Duisburg-Essen. Further, from 1984-1986 he served as vice-chairman, and from 1986-1988 as chairman, of the Department of Physics.


Picture taken during the ICAME 1989 in Budapest, Hungary. From right to left: T. Shinjo, K. Hisatake, W. Keune, T.Toriyama, K. Mibu, N. Hosoito and Mrs. Hisatake.

Werner has been always attracted to Japanese science and culture. In 1979 he spent a sabbatical at the Research Reactor Institute of the Kyoto University, Japan, with Professor Yutaka Maeda as his host. Based on the year-long cooperation with his friend Professor Teruya Shinjo, Kyoto University and the University of Duisburg signed an official agreement of cooperation in 1984. In the following years, a regular fruitful exchange of graduate students, post-docs, and faculty staff took place, and three international “Kyoto-Duisburg Workshops” on magnetic thin films and multilayers were organized. Professors Ko Mibu, Teruo Ono, Takeshi Emoto, Nobuyoshi Hosoito, and Saburo Nasu, all reputed Mössbauer scientists, stayed in Professor Keune’s laboratory for some time.

Werner Keune also enjoyed working in laboratories in other countries. In 1991 he spent a sabbatical at the California Institute of Technology in Pasadena, USA, with Professor Brent Fultz as his host, and worked on Mössbauer diffraction. In 1996 he had a sabbatical stay first at the Laboratoire de Magnetism, C.N.R.S., in Grenoble (France), hosted by Dominique Givord, and later at the Materials Science Division, Argonne National Laboratory at Argonne (USA) in the group of Sam D. Bader, where he studied epitaxial fcc-Fe ultrathin films on diamond C(001).


Werner Keune with graduate students (from left) Ellen Schuster, Balaram Sahoo, and Robert Peters in Chicago during a visit to the Advanced Photon Source at the Argonne National Laboratory, in November 2003.
At Argonne, the Advanced Photon Source had just begun to operate, and Ercan Alp, group leader at the nuclear resonance beamline, invited Werner to cooperate on nuclear resonance inelastic X-ray scattering (NRIXS) experiments on thin films and multilayers. The first successful NRIXS experiments on thin films were performed at that time [12]. In cooperation with the beamline staff, Werner and his group measured the vibrational density of states of 57Fe and 119Sn atoms in various crystalline and amorphous binary alloy films and multilayers. Anomalous non-Debye-like low-energy vibrational excitations in amorphous alloy films [13], phonon confinement in multilayers [14], and metastable interfacial alpha-Sn in Sn/Si multilayers [15] have been investigated by NRIXS.

In the new millenium, Werner Keune has focused his research on NRIXS and on the determination of the Fe spin structure in magnetic heterostructures by Mössbauer spectroscopy. The use of the 57Fe probe-layer technique, combined with conversion electron Mössbauer spectroscopy, allowed the study of the chemical state and spin structure at buried interfaces in exchange-biased ferromagnetic/antiferromagnetic bilayers, such as Fe/FeSn2 [16,17] and Fe/MnF2 [18]. Werner has also demonstrated the usefulness of 57Fe probe-layer CEMS for the characterization of buried interfaces in spintronics materials, such as Fe/GaAs [19,20], and Fe/GaAs-based HEMT heterostructures [21].

Recently, Werner Keune and Ashok Date (India) began joint research activities on nanomagnetic materials. In particular, metastability of cations at the crystallographically inequivalent lattice sites in nanoferrites (soft chemical approaches) is being pursued using a variety of physico-chemical techniques. Werner also recently started collaborations with Professor Beatriz Roldan Cuenya (Department of Physics, University of Central Florida, USA) on the atomic vibrational dynamics of self-organized isolated nanoparticles and with Professors George Filoti and Victor E. Kuncser (Bucharest, Romania) on Mössbauer studies of magneto-electronics materials.

Werner Keune (seated) and Ashok Date in Werner's office at Duisburg in 2006

Werner Keune has published about 200 papers, about 185 of them dealing with Mössbauer spectroscopy. He retired from the University of Duisburg-Essen in January 2006. Werner plans to continue his research interests in thin films, surfaces,  interfaces, and nanoparticles, working with Mössbauer spectroscopy in cooperation with other groups. Recently, he accepted an appointment as Distinguished Visiting Professor at the University of Central Florida (USA) for the Spring term in 2007. His hobbies are occasional tennis with his son Philipp, golf, foreign languages, and, above all, playing with his four-year old granddaughter Clara in his daughter Christina’s apartment in Cologne.

From the very beginning of his research activities, Werner and his Duisburg Mössbauer Group have been a source of inspiration to eager coworkers from outside Germany. In fact, his students, post-docs, and academic and technical staff members have always made their visitors feel very comfortable and welcomed by their top-class facilities, warm hospitality, and attention, which may be the greatest gift and benefit to the international Mössbauer community.

References

  1. J. Lauer, et al., Physica B+C 86-88, 1409 (1977).
  2. W. Keune, et al., J. Appl. Phys. 48, 2976 (1977).
  3. T. Shigematsu, et al., Phys. Rev. Lett. 45, 1206 (1980).
  4. S. Kruijer, et al., Appl. Phys. Lett. 70, 2696 (1997).
  5. M. Walterfang, et al., Appl. Phys. Lett. 76, 1413 (2000).
  6. J. Lauer and W. Keune, Phys. Rev. Lett. 48, 1850 (1982).
  7. R. A. Brand, et al., Phys. Rev. B 31, 1630 (1985).
  8. W. A. A. Macedo and W. Keune, Phys. Rev. Lett. 61, 475 (1988).
  9. R. D. Ellerbrock, et al., Phys. Rev. Lett. 74, 3053 (1995).
  10. T. Ezawa, et al., Physica B 161, 281 (1989).
  11. J. Tappert, et al., Europhys. Lett. 46, 238 (1999).
  12. W. Keune and W. Sturhahn, Hyperfine Interact. 123/124, 847 (1999).
  13. W. Keune, et al., J. Phys.: Condens. Matter 16, S379 (2004).
  14. T. Ruckert, et al., Hyperfine Interact. 126, 363 (2000).
  15. B. Roldan Cuenya, et al., Phys. Rev. B 64, 235321 (2001).
  16. V. E. Kuncser, et al., J. Appl. Phys. 97, 063513 (2005).
  17. F. Stromberg, et al., Phys. Rev. B 72, 064440 (2005).
  18. W. A. A. Macedo, et al., Phys. Rev. B 70, 224414 (2004).
  19. E. Schuster, et al., Superlattices Microstruct. 37, 313 (2005).
  20. M. Doi, et al., J. Magn. Magn. Mater. 240, 407 (2002).
  21. B. Roldan Cuenya, et al., Appl. Phys. Lett. 82, 1072 (2003).

The Editors would like to acknowledge Professor Werner Keune and Professor S. K. Date for their contribution of this story, and to thank Professor Keune for providing the photographs.


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