Discussion journal of the Mössbauer Community

["Nagy, Denes Lajos" <nagy.denes AT wigner.mta.hu>]

Dear Colleagues,

our dear friend and colleague, the pioneer of high-pressure Mössbauer 
spectroscopy, Professor Moshe Paz-Pasternak passed away on 27 October 
2018. We will remember him. Our thoughts are with his family.

An obituary by Gregory Rozenberg and Eran Greenberg also published at the 
IBAME web site ibame.org follows.

    Dénes L. Nagy
     Editor, MIX

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In memoriam: Prof. Moshe Paz-Pasternak (1937-2018)

Prof. Moshe Paz-Pasternak passed away on 27.10.2018.

Prof. Pasternak 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 Mõssbauer 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