MAGNETIC DIPOLAR AND ELECTRIC QUADRUPOLE EFFECTS ON THE MÖSSBAUER SPECTRA OF MAGNETITE ABOVE THE VERWEY TRANSITION

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Submitted on 1 Jan 1979

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MAGNETIC DIPOLAR AND ELECTRIC

QUADRUPOLE EFFECTS ON THE MÖSSBAUER SPECTRA OF MAGNETITE ABOVE THE VERWEY

TRANSITION

L. Häggström, H. Annersten, T. Ericsson, R. Wäppling, W. Karner, S.

Bjarman

To cite this version:

L. Häggström, H. Annersten, T. Ericsson, R. Wäppling, W. Karner, et al.. MAGNETIC DIPOLAR

AND ELECTRIC QUADRUPOLE EFFECTS ON THE MÖSSBAUER SPECTRA OF MAGNETITE

ABOVE THE VERWEY TRANSITION. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-327-

C2-327. �10.1051/jphyscol:19792115�. �jpa-00218485�

JOURNAL DE PHYSIQUE

Colloque C2, suppl6meni au n

Tome

mars 1979, page C2-327

MAGNETIC D I P O L A R AND E L E C T R I C QUADRUPOLE E F F E C T S ON THE M ~ S S B A U E R SPECTRA OF M A G N E T I T E ABOVE T H E VERWEY T R A N S I T I O N

L. ~ Z ~ ~ s t r ' d m , H. Annersten, T. Ericsson, R. ~Zppling, W. Karner and S. Bjarman I n s t i t u t e of Physics, University of (IppsaZo, UppsaZa, Sweden.

Resume.- La magnetite Fe3Or est etudiee par spectromCtrie M'dssbauer entre 120 et 880 K. En-dessous de Tc les spectres sont analyses en 3 sextuplets : 2 pour les sites octaedriques B,et 1 pour les sites tgtraedriques A . Les champs magndtiques sont compares aux mesures d'aimantation par diffraction des neutrons. Dans l'gtat paramagnltique, on observe une correlation interessante entre les dependences thermiques de la resistivite electrique et des dsplacements isomeriques.

Abstract.- Miissbauer spectroscopic studies of powdered FesOc have been undertaken between 120 K and 880 K. Below the magnetic transition temperature (Tc=839.5 K) three six line patterns have been fitted to the experimental spectra. TWO patterns are ascribed to the octahedral B-site and one pat- tern is ascribed to the tetrahedral A-site. It is shown that the broadening of the B-pattern is caused by the presence of two unresolved components. The corresponding ~'dssbauer patterns have in- tensity ratio 3:1 arising from the different magnetic dipolar and electric quadrupolar interactions on the B-site iron ions. It can therefore be concluded that line broadening due to electron hopping between B-sites ions is negligible. The temperature variation of the magnetic fields is found to be proportional to the sublattice magnetization as measured by neutron diffraction. The difference in the magnetic fields at the two nonequivalent B-sites is measured to be 1.1. T at 310 K in good agreement with values found from NMR studies. In the paramagnetic state the electric quadrupole splittings of iron at A and B-site are found to be constant, independent of temperature, having the values zero and 0.16 mm/s, respectively. The centroid shifts, on the other hand show above 700 K large deviations from the calculated second order Doppler shift. It is proposed that the deviations arise from a variation in band overlap. The unusual variation of the centroid shifts can be correla- ted with the observed maximum of the resistivity found for magnetic at about 750 K. The isomer shift variation is most pronounced for A-site which indicates that a model describing the high temperature conductivity in magnetic has to take into account not only the B-sites but also the A-sites.

Temperature dependence of the conductivity of Fe304 (from Parker and Tinslev. Phvs. Status solidi- (a)

&

189.

Centroid shift 6 as a function of temperature. 6 is related to metal- lic iron at RT. Dashed lines show the expected second order Doppler shift with the source at RT.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792115