382
M. Reissner
be obtained by high field Mössbauer spectroscopy [8, 9]. Tuning the field strength
in such way that the magnetic and electrostatic hyperfine interaction is of similar
strength, the sign of the electric field gradient can be obtained for 3/2 → 1/2 transitions, which is not possible without field [10, 11]. This helps to get information
about the charge density distribution and to compare with theoretical calculations.
Especially for intermetallic compounds high external fields are necessary, because
with fields which can be produced by electromagnets (max 2 T) the resolution of the
spectra is too less, to allow clear conclusions.
In this tutorial the possible great extension of knowledge about magnetic behaviour
in solids by application of an external magnetic field is discussed. It is not a review
about the field but should give an insight into what is possible on different levels of
complexity of magnetic structures. Therefore the presented examples are all from
work in which the author was involved. The focus is not only on the results of such
investigations but also on how to come to these results, by also discussing possible
misinterpretations. In the first part the influence of an external field on the hyperfine
interactions and spectral shape is discussed. In the Applications examples from very
simple to extremely complex magnetic structures are presented. The last part is
devoted to the investigation of dynamic effects by high-field Mössbauer spectroscopy.
This tutorial should convince that the investment in a high-field Mössbauer apparatus
makes sense and should help to enter the field.
8.2 Hyperfine Field
From the three main hyperfine interactions which are detectable by Mössbauer spectroscopy the most important one for investigating the magnetic ground state properties is the magnetic hyperfine interaction. It is present if the Mössbauer nucleus
has a nuclear spin I > 1, because in that case it has a dipole moment μ capable to
interact with a magnetic field, which might be present at the site of the nucleus. This
field can be an internal one, due to the surrounding of the nucleus, or an external
one. The magnetic hyperfine field H h f , which the nucleus senses, and which causes
the nuclear Zeemann splitting, has two main components
H h f = H e f f + H loc
(8.1)
with H e f f the effective hyperfine field, and H loc the local hyperfine field. Both can
be decomposed into more fields, according to their origin
H e f f = H c + H O + H d
(8.2)
with H c the Fermi contact field, H O the orbital field, and H d the dipole field and
H loc = H ext + H DM + H L
(8.3)
M. Reissner
be obtained by high field Mössbauer spectroscopy [8, 9]. Tuning the field strength
in such way that the magnetic and electrostatic hyperfine interaction is of similar
strength, the sign of the electric field gradient can be obtained for 3/2 → 1/2 transitions, which is not possible without field [10, 11]. This helps to get information
about the charge density distribution and to compare with theoretical calculations.
Especially for intermetallic compounds high external fields are necessary, because
with fields which can be produced by electromagnets (max 2 T) the resolution of the
spectra is too less, to allow clear conclusions.
In this tutorial the possible great extension of knowledge about magnetic behaviour
in solids by application of an external magnetic field is discussed. It is not a review
about the field but should give an insight into what is possible on different levels of
complexity of magnetic structures. Therefore the presented examples are all from
work in which the author was involved. The focus is not only on the results of such
investigations but also on how to come to these results, by also discussing possible
misinterpretations. In the first part the influence of an external field on the hyperfine
interactions and spectral shape is discussed. In the Applications examples from very
simple to extremely complex magnetic structures are presented. The last part is
devoted to the investigation of dynamic effects by high-field Mössbauer spectroscopy.
This tutorial should convince that the investment in a high-field Mössbauer apparatus
makes sense and should help to enter the field.
8.2 Hyperfine Field
From the three main hyperfine interactions which are detectable by Mössbauer spectroscopy the most important one for investigating the magnetic ground state properties is the magnetic hyperfine interaction. It is present if the Mössbauer nucleus
has a nuclear spin I > 1, because in that case it has a dipole moment μ capable to
interact with a magnetic field, which might be present at the site of the nucleus. This
field can be an internal one, due to the surrounding of the nucleus, or an external
one. The magnetic hyperfine field H h f , which the nucleus senses, and which causes
the nuclear Zeemann splitting, has two main components
H h f = H e f f + H loc
(8.1)
with H e f f the effective hyperfine field, and H loc the local hyperfine field. Both can
be decomposed into more fields, according to their origin
H e f f = H c + H O + H d
(8.2)
with H c the Fermi contact field, H O the orbital field, and H d the dipole field and
H loc = H ext + H DM + H L
(8.3)