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Precursor synthesis and microwave processing of nickel ferrite nanoparticles
V.K.Sankaranarayanan,C.Sreekumar 한국물리학회 2003 Current Applied Physics Vol.3 No.2, 3
Nickel based ferrites have several applications in microwave components as dense polycrystalline compacts. In this study we haveprepared nickel ferrite nanoparticles by a self-ignition reaction directly from a citrate precursor. XRD patterns and FTIR spectraconrm the formation of single phase nickel ferrite. The sample couples readily with microwaves at ambient temperatures and theresidual carbon present in the self-ignited sample could be removed in a few minutes by microwave treatment. The samples,takes place.. 2002 Elsevier Science B.V. All rights reserved.
Govindan, V.,Joseph Daniel, D.,Kim, H.J.,Sankaranarayanan, K. Elsevier 2019 Dyes and pigments Vol.160 No.-
<P><B>Abstract</B></P> <P>Temperature gradient based unidirectional solution growth set-up was specially designed to felicitate the growth of unidirectional crystals of t-stilbene with cylindrical dimension of 6 cm × 2 cm without the need of post growth machining process for scintillator application. A growth rate of 1 mm/day was achieved along <011> direction. The PXRD establishes the phase purity of the grown material. FT-IR and Micro-Raman spectrometers were utilized to justify the presence of the functional groups of the t-stilbene and anisole (solvent). The recorded narrow aromatic vibrations in FT-IR and Raman ascertain the undetectable limit of solvent inclusion in the grown crystal. Absence of new vibrations other than the expected supports the chemical purity of the crystal. The transparency in visible range establishes the suitability of the material for scintillator application where its characteristic emission wavelength under high energy radiation lies. The thermal stability up to 120 °C without any structural/phase change was evident from TG/DTA. The radioluminescence spectra were carried out under β and γ and found the grown crystal exhibits emissions at 384 and 405 nm which is very similar to the studied photoluminescence characteristics. The scintillation characteristics of the t-stilbene investigated using γ –rays from various radioactive sources such as <SUP>137</SUP>Cs, <SUP>133</SUP>Ba and, <SUP>109</SUP>Cd. The scintillation decay time of the grown crystal also studied using the same <SUP>133</SUP>Cs source and fitted with single exponential component of 12 ns.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Organic scintillator t-stilbene single crystal has been grown by SR method. </LI> <LI> A growth rate of 1 mm/day was achieved along <011> direction. </LI> <LI> RL spectra exhibit emissions at 384 and 405 nm under β and γ excitation. </LI> <LI> Scintillation properties were studied using γ –rays of various radioactive sources. </LI> </UL> </P>
Exchange Bias Modifications in NiFe / FeMn / NiFe Trilayer by a Nonmagnetic Interlayer
S. M. Yoon,V. K. Sankaranarayanan,C. O. Kim,C. G. Kim 한국자기학회 2005 Journal of Magnetics Vol.10 No.3
Modification in exchange bias of a NiFe/FeMn/NiFe trilayer, on introduction of a nonmagnetic Al layer at the top FeMn/NiFe interface, is investigated in multilayers prepared by rf magnetron sputtering. The introduction of Al layer leads to vanishing of bias of the top NiFe layer. But the bias for the bottom NiFe layer increases steadily with increasing Al layer thickness and attains bias (230 Oe) which is greater than that of the trilayer without the Al layer (150 Oe). When the top NiFe layer thickness is varied, exchange bias has highest value at 12 ㎚ thickness for 1 nm thicknes of Al layer. Ion beam etching of the top NiFe layer also leads to an enhancement in bias for the bottom NiFe layer.
상카라나라얀,호영강,김철기,김종오,이의복,Sankaranarayanan, V.K.,Hu, Yong-kang,Kim, Cheol-Gi,Kim, Chong-Oh,Lee, Hee-bok 한국재료학회 2003 한국재료학회지 Vol.13 No.6
Magneto-optic Kerr Effect(MOKE), AFM and magnetoresistance measurements have been carried out on as-deposited and annealed Magnetic Tunnel Junctions(MTJs) with junction sizes 180, 250, 320 and 380 $\mu\textrm{m}$ in order to investigate the correlation among interlayer exchange coupling, surface roughness and junction size. Relatively irregular variations of coercivity $H_{c}$ (∼17.5 Oe) and interlayer exchange coupling $H_{E}$ (∼17.5 Oe) are observed over the junction in as-deposited sample prepared by DC magnetron sputtering. After annealing at $200^{\circ}C$, $H_{c}$ decreases to 15 Oe, while $H_{ E}$ increases to 20 Oe with smooth local variation. $H_{E}$ shows very good correlation with surface roughness across the junction in agreement with Neel's orange peel coupling. The increasing slope per $\mu\textrm{m}$ of normalized $H_{c}$ and $H_{E}$ are same near junction edge along free-layer direction irrespective of junction size, giving relatively uniform $H_{c}$ and $H_{ E}$ for wider junction size. Thickness profiles of the junctions measured with $\alpha$-step show increasingly flat top surface for larger junctions, indicating better uniformity for large. junctions in agreement with the normalized$ H_{c}$ and H$/_{E}$ curves. TMR ratios also increase with increasing junction size, indicating improvement for larger uniform junctions.