• D K Mishra

      Articles written in Bulletin of Materials Science

    • Ce-doped LCMO CMR manganites: a consequence of enhanced $T_{c}$ and $T_{\text{IM}}$

      D K Mishra D R Sahu P K Mishra S K Singh B K Mohapatra B K Roul

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      A series of Ce-doped (1–20 mol%) La0.67Ca0.33MnO3 (LCMO) sintered (1400°C) ceramic samples were prepared by the solid-state reaction route. The significant enhancement of metal insulator transition temperature ($T_{\text{IM}} \approx$ 280 K) and Curie transition temperature ($T_{c} \approx$ 270 K) associated with LCMO system by the addition of 10 mol% of Ce has been observed. Further interesting observation showed that both low (≈ 1 mol%) and high (≥ 15 and 20 mol%) level of Ce-doping in LCMO reduced the $T_{\text{IM}}$ appreciably from 280 K to 220 K, and from 100 to 160 K, respectively exhibiting the signature of a unique spin glass transitions at around 30 K. Structural and spectroscopic studies revealed that unreacted CeO2 and MnO2 phases are found to be present in 1, 15, 20 mol% Ce-doped LCMO samples, which is one of the reasons why they show spin glass transition at low temperature. Our present results on bulk Ce-doped (10 mol%) LCMO are found to be encouraging as far as $T_{\text{IM}}$ of epitaxial La0.7Ce0.3MnO3 thin film ($T_{\text{IM}} \approx$ 250 K) is concerned. This finding suggests that single-phase materials of Ce-doped (10 mol%) LCMO can be prepared with enhanced $T_{\text{IM}}$ effectively using solid-state reaction route.

    • Low energy ion beam modification of Cu/Ni/Si(100) surface

      S K Parida V R Rmedicherla D K Mishra S Choudhary V Solanki Shikha Varma

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      Cu/Ni bilayer has been prepared by thermal evaporation of pure Cu and Ni metals onto Si(100) surface in high vacuum; it was sputtered using argon ion beam in ultra-high vacuum. The ion beam-induced surface and interface modification was investigated using X-ray photoelectron spectroscopy and atomic force microscopy techniques. The deposited sample exhibits the formation of CuO nano-structures of size 40 nm on Cu surface and after sputtering with argon ion beam at a fluence of 5 × 1015 ions/cm2, the surface exhibits a mound structure with an average size of about 100 nm. Interestingly, with sputtering at higher fluence of 2.4 × 1016 ions/cm2, the surface exhibits broad pits of sizes ranging from 100 to 300 nm with an average depth of 10 nm. Bottom surface of these pits contains Ni atoms. The Cu 2𝑝3/2 peak exhibits a shift of 0.3 eV towards high binding energy and also a large asymmetry of 0.11 after sputtering at high fluence compared with pure copper. These changes are attributed to Cu–Ni interactions at the interface.

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