• J Kumar

      Articles written in Bulletin of Materials Science

    • Photoinduced fabrication of complex surface relief structures on azobenzene functionalized polymers

      J Kumar L Li Nirmal K Viswanathan S Bian S Balasubramanian D Y Kim S K Tripathy

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      Light induced fabrication of complex surface relief structures on azobenzene functionalized polymers is reported. Large class of side chain and main chain polymers can be utilized to record these relief structures. The recording and erasure process are strongly dependent on the polarization. Possible transport mechanism of polymer chains well below the glass transition temperature due to photoinduced effect is discussed.

    • Studies on structural and magnetic properties of NdFeO$_3$ single crystals grown by optical floating zone technique


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      NdFeO$_3$ single crystals have been grown by optical floating-zone technique using Nd$_2$O$_3$ and Fe$_2$O$_3$ as the source by solid-state reaction method. The crystalline structure of NdFeO$_3$ belongs to orthorhombic symmetry and the presence of a distorted perovskite structure was confirmed by powder X-ray diffraction (XRD) analysis. From the XRDresults, it is visualized that the lattice expansion has been observed in the unit cell parameters which may appear due to interstitial defects in the NdFeO$_3$ matrix. The deficiency of oxygen atoms and the presence of excess Fe ions in NdFeO$_3$ have been confirmed with EDX spectra. The spin-reorientation region ($T=120$ K) exhibits lower coercive field and the hysteresis loops depict enhanced magnetization ($M_{\rm s}$ and $M_{\rm r}$) values of NdFeO$_3$ single crystal. Presence of compensation temperature point at $T_{\rm comp} = 7.5$ K denotes the anti-parallel alignment of rare-earth ions with Fe magnetic moments. At high temperatures, Fe$^{3+}$ magnetic moments show strong antiferromagnetic interactions ensuing in Neel temperature ($T_{\rm N}$)at 690 K.

    • Theoretical investigation on the electronic and optical properties of BSTS compounds with SOC and TB_mBJ potentials


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      In this study, we report on electronic and optical properties of the bulk and primitive structure of A$_2$B$_3$(A = Bi or Sb and B = Se or Te) compounds using FP-LAPW method within density functional theory. The potentials for exchange and correlation is treated within generalized gradient approximation-Perdew Burke Ernzerhof and Tran-Blahamodified Becke–Johnson (TB_mBJ). The inclusion of spin-orbit coupling approximation is used to calculate electronicstructures and optical properties by determining the complex dielectric function, from which the other parameters arederived. The obtained results are in good agreement with the experimental results. Also, Sb$_2$Te$_3$ compounds have beenfound to possess maximum value of absorption and reflection among all the studied compounds. For all the compounds, astrong absorption coefficient ($\alpha$) exists between the energy range 0 and 5 eV, and is greater than 10$^5$ cm$^{–1}$, which makesthem suitable for optoelectronic applications.

    • Investigations on the structural and magnetic properties of Nd$_{1-x}$Gd$_x$FeO$_3$


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      We report on the increase in spin re-orientation transition temperature (T$_{SR}$) and Neel temperature (T$_N$) in Nd$_{0.95}$Gd$_{0.05}$FeO$_3$ compound, by substituting Gd$^{3+}$ ions at the A-site of NdFeO$_3$. Structural and magnetic properties ofNd$_{1-x}$Gd$_x$FeO$_3$ (x = 0, 0.03 and 0.05 mol%) have been analysed by employing solid-state reaction method. Crystallite size reduction and lattice contraction have been observed with increase in Gd substitution in NdFeO$_3$. $M–H$ curves depictstrong ferromagnetic behaviour of Nd$_{1-x}$Gd$_x$FeO$_3$ with a non-saturating and large coercive hysteresis loops. The crystallite size of Nd$_{1-x}Gd$_x$FeO$_3$ influences the magnetic property, resulting in the ferromagnetic behaviour with higher M and Hc values at room temperature and low temperatures

    • Investigation on the structural and magnetic properties of M$_x$Bi$_{2–x}$Te$_3$ (M = Gd, Fe, Cr) (x = 0, 1) using colloidal hot-injection method


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      Gadolinium-doped bismuth telluride (GBT), ferric-doped bismuth telluride (FBT) and chromium-doped bismuth telluride (CBT) nanocrystals have been synthesized using colloidal hot-injection method with same doping ratio. Field-oriented uniaxial anisotropic ferromagnetic properties for all the samples were analysed from the squareness ratio ($M_r$/$M_s$), $K_1$ (magnetocrystalline anisotropic constant), $K_1$$^v$ (shape anisotropic constant), $K_{eff}$ (effective anisotropy constant) and magnetic energy using vibration sample magnetometer. The magneto-impedance (MI) spectral ratio (${\Delta}$Z/$Z_0$)% has been influenced by rotational magnetization, as well as domain wall motion with respect to applied magnetic field. The results have proven that the GBT thin film sample exhibits the maximum MI effect. Our results may shed light on the simple method of synthesis and development of the effective MI materials based on rare-earth/transition-doped bismuth telluride for the realization of magnetic sensor applications in future.

    • Effect of carbon co-doping on magnetic properties of transition and rare-earth metal-doped bismuth telluride


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      We investigated the magnetic interaction of carbon (C)-transition (Cr/Fe) and rare-earth Gadolinium (Gd) metal co-doped bismuth telluride (BT) systems (Cr$_x$C$_y$Bi$_{12-x}$Te$_{18-y}$, Fe$_x$C$_y$Bi$_{12-x}$Te$_{18-y}$ and Gd$_x$C$_y$Bi$_{12-x}$Te$_{18-y}$ (x = 1,y = 1) supercell structures) by using the density functional theory based on the full-potential linear augmented plane wave method via inclusion of spin polarized calculation. Addition of metal dopant ions in bismuth telluride enhanced the totalspin magnetic moment of the entire system ($M_{tot}$), which was further increased by the presence of the carbon ion. However, spin magnetic moment of individual dopant ions ($M_S$) was found to be increased or decreased depending upon the position of the metal-carbon dopants relative to each other. This increase in $M_S$ is explained by Zener exchange mechanism. C showed a weak $M_S$, in its addition in the BT system. Gd-C co-doping showed highest $M_{tot}$ and $M_S$ compared to Fe-C doped (BT) system. The spin magnetic moment of the system and that of individual dopant ions is influenced by varying the position of C relative to metal dopant ions in BT system. This understanding over the changes inthe value of magnetic moment with respect to the position of C ion compared to other dopant ions in the material will lead to the future improvement of magnetic data storage devices.

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    • Dr Shanti Swarup Bhatnagar for Science and Technology

      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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