High Field Mössbauer Spectroscopy

Abstract

Actuellement des champs magnétiques extérieurs variant entre quelques kOe et 150 kOe sont couramment utilisés en spectroscopie Môssbauer. Dans cet article on passe en revue les possibilités offertes par l'adjonction à un spectromètre Môssbauer classique d'une bobine produisant un champ magnétique intense. Les principales caractéristiques d'expériences typiques ainsi que les récents développements de la spectroscopie Môssbauer sous champ intense sont discutés.

Iron(III) oxide polymorphs and their manifestations in in-field [sup 57]Fe Mössbauer spectra

“…Instead, we observe only one triplet spectral component with a value of the effective hyperfine magnetic field close to that of the external magnetic field (see Table 1). This behavior is expected for paramagnetic materials when the external magnetic field slows down the paramagnetic fluctuations of atomic magnetic moments and induces magnetization in the material [29]. In both room-temperature Mössbauer spectra, the spectral contribution of Į-Fe 2 O 3 admixture, identified when refining the respective XRD pattern, is most probably hidden in the signal background.…”

“…Under external magnetic fields, the canting of sublattice magnetizations is intensified. Moreover, in antiferromagnetic materials, when the external magnetic field overcomes a value corresponding to the characteristic spin-flop field, magnetic moments suddenly changes its direction to an orientation antiparallel with respect to that of the external magnetic field [29,30]. In in-field Mössbauer spectra measured in a parallel geometry, this is manifested by enhancement of the 2 nd and 5 th sextet line intensities [29,30].…”

“…Moreover, in antiferromagnetic materials, when the external magnetic field overcomes a value corresponding to the characteristic spin-flop field, magnetic moments suddenly changes its direction to an orientation antiparallel with respect to that of the external magnetic field [29,30]. In in-field Mössbauer spectra measured in a parallel geometry, this is manifested by enhancement of the 2 nd and 5 th sextet line intensities [29,30]. On further increase in the strength of the external magnetic field, the sublattice magnetizations progressively incline towards the direction of the external magnetic field and a gradual decrease in the 2 nd and 5 th sextet line intensities is observed.…”

Velocity driving system for an in-field Mössbauer spectrometer

“…In order to avoid influences of the external magnetic field, the radioactive source is driven by means of a 0.5 m long non-magnetic rod. Such as arrangement results in a heavy load for the transducer and a large driving force [1]. Unfortunately this setup with the standard PID driving unit [8] is unable to fully stop all spurious effects.…”

“…Unfortunately, the external magnetic field highly influences the transducer performance. Generally it is possible to reduce the moving system errors by appropriate material/distance shielding and/or a suitable feed-back PID (proportional-integral-derivative) controller [1]. The parameters of the PID controller has to be enough flexible to work with external magnetic fields up to 10 T.…”