Electronic Structure and Crystal Field in Sm3Se4 and Sm3Te4
The Th3P4 cubic crystal R3X4 (X denotes S, Se or Te) with Eu and Sm for R are interesting materials because the Fermi level is just at the 4f level which is situated in the gap between the conduction and valence bands. The transport of electrons occurs by thermally induced hopping between the equivalent R++ and R+++sites which coexist in the ratio 1:2, respectively. In the case of Eu3S4 this mechanism is supported by the results of a Mössbauer experiment1 in which the shape of the spectra between 83 K and 300 K could be interpreted in terms of valence fluctuations in the time range of 10−7−10−11 s. The charge ordering of Eu ++and Eu+++ occurs at a temperature of about 160 K.2 For Sm3X4 compounds, however, the problem is more complex because the charge ordering has not yet been observed even at the lowest temperature down to 1.5 K.3-6 This may mean that some kind of valence fluctuation occurs at the lowest temperature. Furthermore, the data analyses of the magnetic susceptibility presented so far are highly controversia1,3,4,7 again related to the possible existence of valence fluctuations. We have made fairly big single crystals of Sm3Se4 and Sm3Te4, and we examined the above problems more carefully, both experimentally and theoretically.
KeywordsMagnetic Susceptibility Crystal Field Exchange Constant Antiferromagnetic Exchange Inter Action Valence Fluctuation
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