continuation of reduction of exchange interaction and iron magnetic moment to
2.9 µ B (magenta curve). For higher concentration of niobium in the iron surrounding, iron ions become paramagnetic in room temperature (green curve) [74]. It
should also be noted that the reduction of magnetic moment is associated with the
reduction of superexchange interaction and magnetic ordering temperature. The
influence of temperature is visible in the half width of the spectral line. The
parameter is the highest for the Zeeman splitted component, for which two iron ions
in B-sites are substituted by niobium and predicted magnetic ordering temperature
is lower than in case of one Nb
5+ . The broadening of the line is most likely related
to the additional disorder caused by thermal fluctuations of iron magnetic moments.
This suggests that these two components are not in a magnetic saturation and are
approaching magnetic ordering point. The value of the parameter for the last
component is considerably lower, what suggests that it is still in the saturation and
the magnetic ordering temperature for this composition is higher.
It should also be mentioned here that the paramagnetic component is attributed
to the iron in which surrounding is more than two niobium cations. In such case,
magnetic ordering temperature may be below room temperature and can be close to
pure Pb(Fe 0.5 Nb 0.5 )O 3 , for which Néel temperature is about 150 K. The similar
doublet of the similar hyperfine interaction parameter values was observed previously in different solid solutions with BFO [75–77].
9.4 Conclusions
In this chapter, application and usefulness of Mössbauer spectroscopy in structural
studies of the magnetoelectric oxide solid solutions are presented. In the beginning,
a general introduction to the Mössbauer spectrometry has been given. The spectroscopy gives the possibility to determine hyperfine interaction parameters like
isomer shift, quadrupole splitting, and magnetic hyperfine field which are briefly
described. A proper description of the parameters is a very often non-trivial
problem. Application of different calculation methods can be very useful to solve it.
Short description of the possibility of the hyperfine interaction parameters determination based on ab initio calculations is also given. In the next part of the chapter,
problem of coexistence of magnetism and ferroelectricity is presented and structural
conditions of such coexistence are shown. On the selected example of BiFeO 3 –Pb
(Fe 0.5 Nb 0.5 )O 3 , step-by-step analysis of Mössbauer spectrum is shown. Basic
concepts of spectral analysis with application to the structure and magnetic properties are presented. The selected examples allowed demonstrating the usefulness of
57 Fe Mössbauer spectrometry in the understanding of chemical, structural, and
magnetic properties of multiferroic compounds.
296
P. Stoch and A. Stoch
2.9 µ B (magenta curve). For higher concentration of niobium in the iron surrounding, iron ions become paramagnetic in room temperature (green curve) [74]. It
should also be noted that the reduction of magnetic moment is associated with the
reduction of superexchange interaction and magnetic ordering temperature. The
influence of temperature is visible in the half width of the spectral line. The
parameter is the highest for the Zeeman splitted component, for which two iron ions
in B-sites are substituted by niobium and predicted magnetic ordering temperature
is lower than in case of one Nb
5+ . The broadening of the line is most likely related
to the additional disorder caused by thermal fluctuations of iron magnetic moments.
This suggests that these two components are not in a magnetic saturation and are
approaching magnetic ordering point. The value of the parameter for the last
component is considerably lower, what suggests that it is still in the saturation and
the magnetic ordering temperature for this composition is higher.
It should also be mentioned here that the paramagnetic component is attributed
to the iron in which surrounding is more than two niobium cations. In such case,
magnetic ordering temperature may be below room temperature and can be close to
pure Pb(Fe 0.5 Nb 0.5 )O 3 , for which Néel temperature is about 150 K. The similar
doublet of the similar hyperfine interaction parameter values was observed previously in different solid solutions with BFO [75–77].
9.4 Conclusions
In this chapter, application and usefulness of Mössbauer spectroscopy in structural
studies of the magnetoelectric oxide solid solutions are presented. In the beginning,
a general introduction to the Mössbauer spectrometry has been given. The spectroscopy gives the possibility to determine hyperfine interaction parameters like
isomer shift, quadrupole splitting, and magnetic hyperfine field which are briefly
described. A proper description of the parameters is a very often non-trivial
problem. Application of different calculation methods can be very useful to solve it.
Short description of the possibility of the hyperfine interaction parameters determination based on ab initio calculations is also given. In the next part of the chapter,
problem of coexistence of magnetism and ferroelectricity is presented and structural
conditions of such coexistence are shown. On the selected example of BiFeO 3 –Pb
(Fe 0.5 Nb 0.5 )O 3 , step-by-step analysis of Mössbauer spectrum is shown. Basic
concepts of spectral analysis with application to the structure and magnetic properties are presented. The selected examples allowed demonstrating the usefulness of
57 Fe Mössbauer spectrometry in the understanding of chemical, structural, and
magnetic properties of multiferroic compounds.
296
P. Stoch and A. Stoch