CONVERSION ELECTRON MEASUREMENTS OF CORE POLARIZATIONS IN IRON METAL
Le Journal de Physique Colloques
The polarizations of 2s and 3s/4s electron spin densities at the 57 Fe nucleus in iron metal are being remeasured. The present result for the 2s electrons is tZV'2s+^0^/^Is^.^°^-'Zl = "0.0077 ±0.0040. These results are shown to agree with observed multiplet structure in X-ray photoemission. The two spectroscopies give different results for 3s electrons, however. In 1972 first results were published /1,2/ of a direct measurement of the spin dependence of the electron density at the 57 Fe nucleus
... in iron metal and Fe203. In our laboratory we are carrying out a new improved version of this experiment /3-6/. Here only a brief description will be given. In essence the Mossbauer effect is used to excite either the (-1/2 to -3/2) or the (1/2 to 3/2) transition in an absorber nucleus. The former occurs at maximum negative resonance velocity and gives rise to line 1 of the normal six line spectrum, and the latter occurs at maximum positive velocity and gives rise to line 6. These transitions are detected by observing the internal conversion electrons. The electrons corresponding to line 1 have initial spin direction up in the atom, i.e., parallel to the majority d electron spin, and those corresponding to line 6 have initial spin down. Since the internal conversion coefficient is proportional to the electron density at the nucleus, iji 2 (0), it is possible to determine the spin dependence of ij; (0) from the intensities of lines 1 and 6. The electrons are further separated in an energy analyzer before detection so that the spin densities may be determined for the different atomic shells individually. The results for the n atomic shell are expressed in terms of where N is the electron count rate and a the inn n ternal conversion coefficient of the s electrons if the p electrons are neglected. At present the value obtained in our ongoing remeasurement of iron metal is, for the L shell, 6 = -0.0071±0.0037. The Pi/2,3/2 electrons make a small but non-negligible contribution to this result. If for lack of a better estimate they are assumed to have zero polarization, one finds 6 2g = -O.0O77±O.0O4O. A 2p polarization as large as 1 percent would change 6» by only 0.001. This result agrees with the earlier value /2/ of 6 2g = -0.0063±0.0015. These values are about a factor of three larger in magnitude than various theoretical calculations /7,8/ and correspond to a contribution to the internal magnetic field at the nucleus of about -1600 kG. At our present state of understanding of hyperfine interactions in solids there does not seem to be any positive contribution large enough to result in the well known value for the total internal field in iron metal of -330 kG at 298 K. It is important, therefore, to reexamine in detail the assumptions upon which the interpretation of the experiment is based. We have considered several influences but only the one reported here has so far proved significant. It is observed that in X-ray photoelectron spectroscopy (XPS) of 2s and 3s electrons in 3d transition metal compounds /9,10/ the spectra show a satellite structure attributed to the exchange interaction between the remaining unpaired s electron and the unfilled 3d shell. For example, the ground states of the ions Fe 3+ and Mn 2+ are 6 S due to the (core) 3s 2 3p 6 3d s configuration. Creation of a Is, 2s or 3s hole while keeping the remaining orbitals frozen results in 7 S and 5 S ion states, the former when a spin down electron is removed and the latter when fSupported by the National Science Foundation under grant DMR77-09911. JOURNAL DE PHYSIQUE Colloque C2, supplément au n° 3, Tome 40, mars 1979, page C2-188 Résume.-Les polarisations de spin des électrons 2s et 3s/4s au noyau 57 Fe du fer métallique ont été remesurées. Pour les électrons 2s on a trouvé ]j ; 2s-t'( 0 )/ , '4s4-( 0 )~1 = ~0,0077±0,0040. Ces résultats sont conformes à l'observation de la structure du multiplet en photoémission des rayons X. Cependant, les deux spectroscopies donnent des résultats différents pour les électrons 3s. Article published online by EDP Sciences and available at http://dx.