42
R. Rüffer and A. I. Chumakov
Fig. 1.20 Magnetic landscape in a Nb foil where an array of micro Hall probes (white dots) detect
avalanches coming down the slope of the largest flux ridge. The intensity along the vertical axis is
proportional to the magnetic field inside the sample (Reprinted figure with permission from [127],
Copyright (2004) by the American Physical Society)
1.7.1.4 Nano-imaging
Besides its sensitivity to magnetic structures, nuclear resonance scattering is an established tool to monitor chemical and oxidation states of solids. This enables imaging
of chemical and valence structures in real space.
In imaging chemical and oxidation profiles, the mission of nuclear resonance
beamlines is to study systems with highly complex micro-size spatial composition.
One of the most challenging scientific cases in this aspect are studies of meteorites.
Meteorites are slowly cooled (2–9 K per million years) systems, most often consisting
of olivine crystals in an Fe-Ni matrix originating from the mantle of a 200-km-radius
asteroid [129]. They carry the time-resolved geological, thermal, and magnetic history of the Universe. One of the most intriguing items of these systems is the so-called
cloudy zone (CZ), a nanoscale intergrowth of tetrataenite (ordered FeNi) islands of
10–200 nm in size embedded in an Fe-rich matrix, which reveals the time-series
record of magnetic activity on an asteroid body. With the current available 10 μm
spatial resolution in SMS spectroscopy our understanding of meteoritic metal could
already be improved by allowing the cloudy zone to be measured separately from the
surrounding metal phases [128]. Scanning along the line crossing the cloudy zone
(Fig. 1.21, left panel) is accompanied by drastic changes of the measured Mössbauer
spectra, developing from schreibersite to kamacite and further to plessite contributions (Fig. 1.21, right panel). The available 10 μm spatial resolution reveals that the
plessite region, previously considered to be a pure-chemical state, actually contains
an essential contribution of antitaenite. This finding indicates that the saturation of
magnetization in this regions occurs at much lower temperatures than previously
thought [128].
However, the most intriguing knowledge on the magnetic history of the Universe
is stored in the fine structure of the cloudy zone (Fig. 1.22). The age of the cloudy
zone decreases with the distance from the tetrataenite rim [129]. Thus, performing nano-scale imaging of the magnetic, chemical, and coordination states of the
R. Rüffer and A. I. Chumakov
Fig. 1.20 Magnetic landscape in a Nb foil where an array of micro Hall probes (white dots) detect
avalanches coming down the slope of the largest flux ridge. The intensity along the vertical axis is
proportional to the magnetic field inside the sample (Reprinted figure with permission from [127],
Copyright (2004) by the American Physical Society)
1.7.1.4 Nano-imaging
Besides its sensitivity to magnetic structures, nuclear resonance scattering is an established tool to monitor chemical and oxidation states of solids. This enables imaging
of chemical and valence structures in real space.
In imaging chemical and oxidation profiles, the mission of nuclear resonance
beamlines is to study systems with highly complex micro-size spatial composition.
One of the most challenging scientific cases in this aspect are studies of meteorites.
Meteorites are slowly cooled (2–9 K per million years) systems, most often consisting
of olivine crystals in an Fe-Ni matrix originating from the mantle of a 200-km-radius
asteroid [129]. They carry the time-resolved geological, thermal, and magnetic history of the Universe. One of the most intriguing items of these systems is the so-called
cloudy zone (CZ), a nanoscale intergrowth of tetrataenite (ordered FeNi) islands of
10–200 nm in size embedded in an Fe-rich matrix, which reveals the time-series
record of magnetic activity on an asteroid body. With the current available 10 μm
spatial resolution in SMS spectroscopy our understanding of meteoritic metal could
already be improved by allowing the cloudy zone to be measured separately from the
surrounding metal phases [128]. Scanning along the line crossing the cloudy zone
(Fig. 1.21, left panel) is accompanied by drastic changes of the measured Mössbauer
spectra, developing from schreibersite to kamacite and further to plessite contributions (Fig. 1.21, right panel). The available 10 μm spatial resolution reveals that the
plessite region, previously considered to be a pure-chemical state, actually contains
an essential contribution of antitaenite. This finding indicates that the saturation of
magnetization in this regions occurs at much lower temperatures than previously
thought [128].
However, the most intriguing knowledge on the magnetic history of the Universe
is stored in the fine structure of the cloudy zone (Fig. 1.22). The age of the cloudy
zone decreases with the distance from the tetrataenite rim [129]. Thus, performing nano-scale imaging of the magnetic, chemical, and coordination states of the