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Moshe Paz-Pasternak (1937-2018) (29/10/18)

Prof. Moshe Paz-Pasternak passed away on Saturday, Oct. 27, 2018. He received his PhD from the Weizmann Institute of Science (1967), and held postdoctoral fellowships at the University of Illinois, Urbana, before becoming a staff member at the School of Physics and Astronomy of the Tel Aviv University (Senior Lecturer 1970, Associate Prof. 1976, Full Prof. 1983).

Since 1976 he has held several visiting professorships in University of California, Santa Barbara; Catholic University Leuven; Los Alamos National Laboratory; University of California, Berkeley; Osaka University; Max Planck Institute, Stuttgart.

Moshe has spent most of his professional career working on various aspects of the Mössbauer effect. He has used the Mössbauer effect to solve important problems in a wide range of fields, from solid-state physics to chemistry and geophysics. Starting from the early 1980s his most effort were in the development of the Mössbauer spectroscopy for magnetic studies at high pressures using diamond anvil cells. The small sample size (<10 mg) and substantial attenuation of the diamonds, even for the 14.4 keV γ-ray of 57Fe, seemed formidable. Attenuation was reduced by choosing a pressurized source and his first project in collaboration with Dr. R. Dean Taylor (Los Alamos NL) became the effect of pressure on iodine using the Mössbauer effect of 129I. A series of pressure experiments including SnI4, GeI4, NiI2, FeI2, and VI2 showed features of metallization, amorphization, quadrupole distortion, isomer shift, and magnetization changes. The collapse of the magnetic hyperfine field with pressure in NiI2 has become the classic demonstration of the Mott transition. Resistivity and XRD measurements soon supplemented the Mössbauer spectroscopy results.

New cell designs, better anvils and new “point sources” have allowed 57Fe and 119Sn MS at ever-higher pressures up to above a megabar. Recently, almost all high-pressure experiments of Prof. Pasternak have involved iron-bearing compounds, including some of interest to the geosciences (R. Jeanloz). Pressure-induced transformations abound in the various systems – metallization, amorphization, structural changes, magnetization collapse, coordination changes, spin crossover, valence modification, and self-oxidation – and the Mössbauer effect served as the primary tool. In the last two decades substantial progress in the study of the Mott-transition phenomenon has been achieved just owing to the significant improvement of the high-pressure technique, particularly high-pressure Mössbauer spectroscopy for magnetic studies and electrical resistivity for probing of transport properties. Remarkable experimental observations pertinent to the study of Mott-transition phenomenon were obtained by the first time by Moshe’s Tel Aviv University HP-group using the above-mentioned methods. Most of these results have also been discussed in a series of review papers.

Gregory Rozenberg, Eran Greenberg