8 Mössbauer Spectroscopy in External Magnetic Fields
395
Fig. 8.14 Sketch of the
variable temperature insert
8.5 Applications
8.5.1 Ga Substituted Co Ferrite
In spinels, general structure formula AB 2 O 4 , magnetic ions are usually distributed
over the octahedral B and the tetrahedral A sites (Fig. 8.15). In case of a two atom
spinel, most prominent representative is magnetite, Fe 3 O 4 . For spinels, where more
than one atom can occupy the A and B sites, the distribution of magnetic atoms over
these sites is one of the important points for understanding the magnetic behaviour. If
all A-atoms are occupying the B-sites and 50% of the B-atoms are on the A-sites than
one has a so-called inverse spinel. In case of not full occupation of A-atoms on the
B-sites one speaks of partial inverse spinel. For example, in case of Ga substituted Co
ferrite no clear picture concerning the site distribution of the three elements Co, Ga,
and Fe was obtained from different measurements. X-ray diffraction investigations
indicated that Co mainly occupies only B-sites, thus suggesting an inverse spinel [38].
In contrast from neutron diffraction measurements on pure CoGa 2 O 4 only 60% of
the Ga atoms were found on the cobalt A-sites, thus pointing to partial inverse spinel
[39].
57 Fe Mössbauer spectroscopy on CoGa 2−x Fe x O 4 at room temperature show two
clearly separated components with different intensities, pointing to a partial inverse
395
Fig. 8.14 Sketch of the
variable temperature insert
8.5 Applications
8.5.1 Ga Substituted Co Ferrite
In spinels, general structure formula AB 2 O 4 , magnetic ions are usually distributed
over the octahedral B and the tetrahedral A sites (Fig. 8.15). In case of a two atom
spinel, most prominent representative is magnetite, Fe 3 O 4 . For spinels, where more
than one atom can occupy the A and B sites, the distribution of magnetic atoms over
these sites is one of the important points for understanding the magnetic behaviour. If
all A-atoms are occupying the B-sites and 50% of the B-atoms are on the A-sites than
one has a so-called inverse spinel. In case of not full occupation of A-atoms on the
B-sites one speaks of partial inverse spinel. For example, in case of Ga substituted Co
ferrite no clear picture concerning the site distribution of the three elements Co, Ga,
and Fe was obtained from different measurements. X-ray diffraction investigations
indicated that Co mainly occupies only B-sites, thus suggesting an inverse spinel [38].
In contrast from neutron diffraction measurements on pure CoGa 2 O 4 only 60% of
the Ga atoms were found on the cobalt A-sites, thus pointing to partial inverse spinel
[39].
57 Fe Mössbauer spectroscopy on CoGa 2−x Fe x O 4 at room temperature show two
clearly separated components with different intensities, pointing to a partial inverse