B. D. Padalia

X-ray absorption spectroscopic study of mixed valence systems EuCu2Si2, YbCu2Si2 and Sm4Bi3

Abstract X-ray absorption spectroscopy technique is employed to determine the valence of the rare earth ions in EuCu 2 Si 2 , YbCu 2 Si 2 and Sm 4 Bi 3 . In each case, two absorption peaks corresponding to two different valence states of respective rare earth ions have been observed. Low temperature (77 K) study of EuCu 2 Si 2 indicates distinct change in the relative intensities of the absorption peaks compared to those registered at room temperature (300 K). It is inferred from the change in the relative intensities that the population of Eu 2+ in EuCu 2 Si 2 decreases at liquid nitrogen temperature compared to Eu 3+ . Conclusions drawn from these results agree well with those reported by others using different experimental techniques. In Sm 4 Bi 3 , Sm 2+ and Sm 3+ are found to occur in the ratio of 3:1.

Some new materials REAl2Ga2 and their NMR and X-ray absorption studies

Abstract New ternary rare earth intermetallic compounds crystallizing in the ThCr 2 Si 2 type structure viz., LaAl 2 Ga 2 , PrAl 2 Ga 2 , NdAl 2 Ga 2 , EuAl 2 Ga 2 and YbAl 2 Ga 2 are reported. The quadrupole coupling constant of 27 Al has been measured for all these samples. The Knight shift of 171 Yb in YbAl 2 Ga 2 is found to be very small ( ⋍0% ) and almost temperature independent. The positions of the L 3 -absorption edge of Eu and Yb in EuAl 2 Ga 2 and YbAl 2 Ga 2 have been measured. These results suggest that Eu and Yb are divalent in character.

Anomalies of resistivity and its T3 -dependence at low temperatures in Eu-based valence fluctuating systems

Abstract Ce-based valence fluctuating systems, in general, are known to exhibit anomalous temperature dependence of resistivity, ϱ(T). In contrast, resistivity measurements have been reported thus far on only two Eu-based valence fluctuating (VF) systems and therefore further investigations are required on such materials. Here we report the results of our measurements of the temperature dependence of the resistance R(T) of three Eu-based VF-systems, viz., EuIr2Si2, Eu2Ni3Si5 and EuNiSi2. The measurements of R(T) have also been carried out in Eu2Au3Si5 and EuNi2Si2, where Eu is divalent and trivalent respectively. These studies reveal an anomalous behaviour of R(T) in the above-mentioned Eu-based VF-systems.

ESCA studies of sputtered amorphous CoNbZr film

Abstract Detailed ESCA studies of sputtered amorphous Coue5f8Nbue5f8Zr film, carried out after a period of one year, reveal that Zr oxidises violently and migrates to the surface. Oxidation of Nb is limited to top layers (∼ 300 A) while Co remains metallic through out the film. The film beyond 600 A down to the substrate interface is quite homogeneous. Such information could be of importance in some applications of these materials.

MAGNETIC AND DIFFUSION STUDIES IN COMPOSITIONALLY MODULATED NI/MN FILMS

Abstract We have prepared compositionally modulated Ni/Mn films by sequential evaporation in ultrahigh vacuum and studied their magnetic properties. For thin layers of the order of 40 A, the magnetic properties change with time but stabilize after a period of about six months. Auger and electron spectroscopy for chemical analysis studied performed on these samples indicate strong diffusion and inter-mixing of nickel and manganese. From the magnetic characteristics, it is seen that in spite of diffusion the samples cannot be considered as a homogeneous alloy.

XPS STUDY OF THE EXCHANGE-SPLITTING IN THE S-LEVELS OF MN AND R IN RMN2SI2 (R = LA TO ND, SM AND GD)

Abstract Exchange (or multiplet) splitting, Δ E s of the 3 s core-level of Mn in RMn 2 Si 2 (R = La to Nd, Sm and Gd) has been observed using XPS technique. The measured value of Δ E s is used to determine the magnetic moment on Mn ion in RMn 2 Si 2 . Δ E s has also been measured for the 4 s and 5 s levels of R in RMn 2 Si 2 and it is found that the value of Δ E s increases with increase in the number of unpaired spins (La to Gd).