Chemistry Reference
In-Depth Information
Fig. 2.39 Variable temperature
151
Eu Mössbauer spectra of the intermetallic compound EuNiP.
Shaded subspectra correspond to Eu
2+
(dark grey) and Eu
3+
(light grey)[
70
]
EuNiP undergoes a Verwey-type charge delocalization transition when heated
above 470 K prior to the structural gamma-beta phase transition at approximately
510 K. This finding confirms the results of photoemission spectroscopy of the iso-
structural compound EuPdP and of TB-LMTO-ASA (Tight-Binding Linear Muffin-
Tin Orbital Atomic-Sphere Approximation) band structure calculations. It has been
proposed that a van Hove singularity associated with a high density of 4f states close
to the Fermi energy plays a particular role in mixed valency pnictide EuNiP [
70
].
2.3.4 Molecular Magnetism
Mössbauer spectroscopy, primarily employing
57
Fe as a nuclear probe, has
developed to an enormously helpful complementary tool supporting standard
SQUID and ac/dc magnetic measurements in studies of magnetic behavior of solid
materials. Magnetic dipole interaction (see
Sect. 2.2.3
) will lead to a magnetically
split Mössbauer spectrum, a sextet in the case of
57
Fe Mössbauer spectroscopy,
provided a local effective magnetic field pointing sufficiently long (longer than the
lifetime of the 14.4 keV nuclear excited state) in a fixed direction. Magnetic
behavior of solid material is usually categorized into two classes: (1) Long-range
