Showing papers by "Sudipta Bandyopadhyay published in 2017"

Application Possibility of Mn 0.04 Cu 0.05 Zn 0.91 O in Electronic and Magnetic Devices

Abstract: In this literature, we have investigated the magnetic properties and Schottky device-based charge transport properties of hydrothermally derived Mn0.04Cu0.05Zn0.91O nanorod. The doping of 3-D transitional metals, Mn and Cu, within ZnO makes it potentially applicable in spin-based electronics, whereas its temperature-dependent conductivity (of the order of 10−3 in C.G.S.) makes it suitable for semiconductor-based devices. The observation of intrinsic ferromagnetism of the synthesized composite and its variation of magnetization with magnetic field and temperature exhibited the suitability of spin-based electronic application. To check the applicability in optoelectronic devices, metal–semiconductor (Al/Mn0.04Cu0.05Zn0.91O) junction was fabricated and analyzed. The current–voltage characteristic represented the rectifying behavior of the junction with on/off current ratio 4.3 at ±1 V in dark and potential barrier height 0.61 eV. The significant change in rectification due to the influence of incident radiation makes this material suitable for photosensing electronic device application.

Cationic order versus La-O covalency in LaA(Ca,Ba)VMoO6 double perovskites

Abstract: We have investigated the structural and physical properties of double perovskite (DP) $\mathrm{La}A{\mathrm{VMoO}}_{6}$ ($A={\mathrm{Ca}}^{2+}$, ${\mathrm{Ba}}^{2+}$; abbreviated as LCVMO and LBVMO from now on) compounds, proposed to be possible half-metallic antiferromagnets (HMAFMs). Here we show that within $\mathrm{La}A{\mathrm{VMoO}}_{6}$ double perovskite structure, La-O covalency competes against $B$-site as well $A$-site cationic order and this competition critically influences their physical properties. Evidently, the presence of ${\mathrm{Ca}}^{2+}$ or ${\mathrm{Ba}}^{2+}$ at the $A$ site along with ${\mathrm{La}}^{3+}$ would offer a tool to modify the $A$-site ordering and consequently influence the La-O covalency as well. Our experimental results reveal that LCVMO lies at the extreme end of this family and accommodates large scale phase separation in terms of La, V, and Ca, Mo-rich phases as a result of dominant La-O covalency. On the other hand, LBVMO is more correctly described as a layered $A$-site ordered and nearly complete $B$-site disordered double perovskite where cationic order dominates the La-O covalency. The general trend of our experimental findings is in agreement with the ab initio electronic structure calculations, carried out on realistic structures based on local coordination obtained from extended x-ray-absorption fine-structure study.

Structural, electronic, morphological, optical and magnetic properties of Mn0.03–xCoxZn0.97O (0 ≤ x ≤ 0.03) nanoparticles

Abstract: Nanoparticles of Mn0.03–xCoxZn0.97O (x = 0.00, 0.01, 0.02, 0.03) have been synthesized using sol–gel technique. The wurtzite structure of ZnO has been confirmed and no impurity phase has been detected in any of the nanoparticle samples. The compositional study exhibits the presence of transition metal (TM) and further X-ray absorption near edge spectroscopy indicates quite low presence of desired Mn2+ ions whereas the presence of desired Co2+ ions is substantial. Morphological patterns have confirmed the formation of nanoparticles and supported the systematic variation of crystallite size as observed from structural study. The estimated band gap exhibits a systematic trend of red shift associated with weak quantum confinement effect and it is commensurate with the variation of particle size. Point defects particularly zinc interstitial (IZn) has been detected from photoluminescence (PL) measurement. Field dependent magnetization (M–H) measurement exhibits room temperature (RT) ferromagnetic (FM) ordering. The temperature dependent magnetization (M–T) measurements demonstrate the presence of simultaneous antiferromagnetic coupling which is responsible for weakening of FM ordering. Moderate temperature (350 °C) annealing has been found to be very effective for achieving RT FM ordering in TM doped ZnO nanoparticles and Co seems to be quite efficient than Mn so far as substitutional replacement of Zn by TM ion is concerned.