J. Phys. Colloques
Volume 40, Numéro C2, Mars 1979
International Conference on The Applications of The Mössbauer Effect
Page(s) C2-233 - C2-233
International Conference on The Applications of The Mössbauer Effect

J. Phys. Colloques 40 (1979) C2-233-C2-233

DOI: 10.1051/jphyscol:1979283


H. de Waard

Laboratorium voor Algemene Natuurkunde, University of Groningen, Netherlands.

Le champ magnétique hyperfin a été mesuré sur des impuretés Cd et Sn substituant Mn dans un alliage de Heusler Pd2Mn0.95.Sn1.05 et comparé aux champs hyperfins mesurés sur les mêmes impuretés substituant Sn. Les signes et les ordres de grandeur diffèrent fondamentalement, mais les variations en fonction de la valence de l'impureté sont parallèles et décalées l'une par rapport à l'autre de ΔZ = 2,0 environ. Ce comportement peut être interprété par le modèle de la charge d'écran dû à Blandin et Campbell.

It was recently found by Le Dhang Khoi et al. / 1 / that the magnetic h.f. field of In impurities substituting Mn in Pd2MnSn differs in sign and magnitude from the field of In impurities in Sn sites. We have extended this investigation to Cd and Sn atoms in the same alloys, prepared with a shortage of a few percent of Mn to allow part of the Cd and Sn atoms to occupy Mn sites. In both cases, we observe two spectral components with different fields, one of which agrees well with the field earlier observed for Cd and Sn atoms on Sn sites. The other component, presumably due to atoms in Mn sites, has a quite different field value. The investigation-of the Cd impurity fields, performed with the TDPAC technique will be reported elsewhere. The Sn fields were determined from Mössbauer spectra of a Pd2Mn0.95Sn1.05 /2/ absorber, using a Ba119mSnO3 source. The fortunate fact that the extra component in the spectrum has a much larger field value than the normal component makes it possible to measure it accurately, despite its small intensity. This is shown in figure 1, where the vertical scale of the large field component has been enlarged 40 times. The absorption depth of this component is 2 percent of that of the small field component. For Cd and In the measurements yield a positive sign for the hyperfine field of the extra component. Assuming the Sn field to be also positive, we see from figure 2, that the fields of Cd, In and Sn in Mn sites establish a clear trend : a rapid increase of the field with impurity atomic number that parallels the behaviour of the field for impurities in Sn sites, but that is shifted to lower Z by about two units. This behaviour can be explained in terms of the charge screening C.E.P. model of Blandin and Campbell /3/.