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- 검색키워드
- 저자 : Kavita Kumari (검색결과 22 건)
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Kumari Kavita,아크샤이 쿠마르,Shin MinJi,Kumar Shalendra,허석환,Koo Bon Heun 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.12
The magnetocrystalline anisotropy and the exchange bias in nanocrystalline FeCo with and without a post-synthesis hightemperature thermal treatment have been investigated. The synthesized products were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and dc magnetization. The XRD spectra revealed the presence of secondary phases which reduced after thermal treatment resulting in the formation of single-phase polycrystalline FeCo. The FE-SEM micrographs confirmed the formation of impurities, which disappeared after thermal treatment, along with the substantial grain growth. The uniform distribution of the elements was confirmed through EDS spectra. The temperature and the magnetic field-dependent magnetization measurements under various conditions showed that, as a consequence of thermal treatment, the saturation magnetization and the magnetocrystalline anisotropy has been enhanced along with the generation of exchange bias. The phenomena of grain growth, formation of grain boundary and the exchange interactions have been described with the help of the proposed mechanism. In brief, the post-synthesis high-temperature thermal treatment induced structural as well as microstructural variations leading to the formation of grain boundaries. These grain boundaries provided interface regions for the occurrence of exchange interactions, which enhanced the magnetocrystalline anisotropy and induced exchange bias in nanocrystalline FeCo.
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Synthesis and characterization of FeCo-Mn₃O₄ hetero-nanostructures
Kavita Kumari,Akshay Kumar,MinJi Shin,Seok Hwan Huh,Bon Heun Koo 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
The magnetic hetero-nanostructures have gained immense attention of the scientific community due to their wide range of applications. The magnetic hetero-nanostructures have been exploited for the exchange bias effect which is highly desirable for the applications like magnetic sensors and non-volatile memory. Therefore, in the present work, the FeCo-Mn₃O₄ nanostructures have been prepared through chemical route method following two-pot synthesis. The heterostructure having the combination of ferromagnetic and antiferromagnetic materials can make an excellent system for the investigation of the exchange bias effect. The synthesized nanostructures were characterized with various characterization techniques such as x-ray diffraction (XRD), high resolution field emission scanning electron microscopy (HR-FESEM), electron dispersive x-ray spectroscopy (EDS) and dc-magnetization. The XRD spectra revealed the presence of cubic FeCo and tetragonal Mn₃O₄. The crystallite size has been calculated with in the nanometer range. The HR-FESEM micrographs demonstrated the formation of non-spherical particles. The histograms revealed a broad particles size distribution indicating that the average particle size remains with in the nanometer range. The EDS images displayed the presence of Fe, Co, Mn and O in the samples. The distribution of elements revealed that the manganese oxide surrounds the FeCo nanoparticles. The magnetic field dependent magnetization shows the ferromagnetic behaviour of the particles as shown by the M-H hysteresis curves. The field cooled and zero-field cooled M-H hysteresis curves evidenced the induced exchange bias effect.
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Effect of hydrazine on structural, morphological and magnetic properties of SmCo-Co nanocomposites
Kumari Kavita,Kumar Akshay,Park Su-Jeong,Sharma Mohit K.,Yadav Naveen,Kumar Manish,Kumar Shalendra,Huh Seok-Hwan,Kim Jong-Woo,Koo Bon-Heun 한국물리학회 2023 Current Applied Physics Vol.53 No.-
In the present work, one-dimensional (1-D) SmCo-Co magnetic nanocomposites are prepared in a single-pot chemical synthesis in the presence of external magnetic field with varying amounts of hydrazine hydrate with samples named as: SC-2 mL, SC-4 mL, SC-6 mL and SC-8 mL. The Rietveld refinement of XRD patterns revealed the formation of Sm2Co17 (P63/mmc), Sm(OH)3 (P63/m) and hcp-Co (P63/mmc) phases. The 1-D nanocomposites are found to possess the highest aspect ratio (~6.3), lowest crystallite size (~49 nm) and highest developed strain (~4.76 x 10-3) corresponding to SC-4 mL. The magnetic response of the samples is found to be affected by the hydrazine amount showing highest saturation magnetization (~156 emu/g) and effective magnetic anisotropy (~1.2 x 106 erg/cm3) for SC-4 mL with highest exchange coupling observed using Bloch law fitting. The results indicate suppressing behaviour of hydrazine amount to be utilized up to a certain limit.
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Kavita Kumari,Akshay Kumar,MinJi Shin,Huh Seok Hwan,Bon Heun Koo 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
The bimetallic nanoparticles as soft magnetic materials possess functional applications due to the low hysteresis losses, large saturation magnetization and high ferromagnetic character. Interestingly, these properties can be optimized in a number of ways. In this paper, the Fe30Co70 nanoparticles were prepared by reducing the precursors using sodium borohydride. The reaction time plays an important part in upgrading the properties of the material. The nanoparticles, prepared with the reaction times: 40min and 10min, were characterized using x-ray diffraction (XRD), low voltage field emission scanning electron microscopy (LV FESEM) and dc-magnetization. The effect of the reaction time was noticeably observed on the structural, morphological and magnetic properties of the nanoparticles. The XRD patterns confirm the formation of single-phase Fe30Co70 nanoparticles with crystallite size in nm range. The low crystallite size was observed for the low reaction time as determined using Scherrer’s formula. The LV FESEM micrographs revealed the spherical shape morphology of the nanoparticles for 10 min reaction time. The nanoparticles were found to form chain-like structures with a reaction time of 40 min. The enhanced ferromagnetic character was observed with the high saturation magnetization at low reaction time. The enhanced reaction time has been found to hamper the magnetic properties of Fe30Co70 magnetic nanoparticles. Thus, the exquisite properties of Fe30Co70 nanoparticles were observed at a reaction time of 10 min, however, they were suppressed as the reaction time was increased to 40 mins.
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Treatment of monazite processed effluent to recover rare earth metals (REMs)
Archana Kumari,Sunidhi Singh,Kavita Parmar,Devendra Deo Pathak,Manis Kumar Jha 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.83 No.-
Improper disposal of effluent generated in rare earth mining areas and ore processing industries resultsin loss of REMs and miserably affects the ecosystem. Thus, their appropriate treatment is required, whichcan be achieved via environmentally feasible processes. In this connection, systematic scientificadsorption studies were carried out to separate REMs using cationic resin, Amberlite IR120 Na from theeffluent generated during monazite processing for REMs recovery. To optimize feasible conditions forREMs recovery, bench scale studies were carried out varying different process parameters viz. pH, contacttime, resin dose, etc. It was observed that adsorption of 92.63% La, 92.79% Ce, 91.45% Nd, 90.95% Pr and95.09% Sm was achieved at aqueous/ resin (A/R) ratio 25 mL/g, pH 1.3 and contact time 10 min. Loadingcapacity of resin was found to hold 48.57 mg REMs/g resin. The adsorption data followed the second orderreaction ((t/q) = (1/h) + (1/qe)(t)) and Langmuir adsorption isotherm (1/q = [(1/k1 qm)(1/Ce)] + (1/qm)). The loaded REMs was effectively eluted using 15% H2SO4 in 10 min. The REMs enriched solution wastreated to get pure REM oxides as precipitate. This technical application will be useful for REMs recoveryas well as to mitigate environmental pollution.
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Akshay Kumar,Kavita Kumari,Minji Shin,Seok Hwan Huh,Bon Heun Koo 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Magnetic refrigeration has attracted significant research interest because of having considerable advantages over the conventional gas compression refrigeration. Unlike the conventional gas compression refrigeration, the magnetic refrigeration is a green cooling technology which does not produce the harmful gases. In the present work, controlled substitution of molybdenum (Mo) in place of Manganese (Mn) was performed in La<sub>1.4</sub>Ca<sub>1.6</sub>Mn<sub>2-x</sub>Mo<sub>x</sub>O<sub>7</sub> (x = 0.0, 0.1, 0.2 and 0.3) to modify the magnetic and magnetocaloric behavior of the material. All samples were prepared through the conventional ceramic heating route. XRD profiles of the synthesized compounds revealed the tetragonal structure (I4/mmm) of bilayer Ruddlesden-Popper (R-P) Phase. However, some MoO<sub>3</sub> oxide and/or unidentified peaks in x ≥ 0.2 doped samples emerged along with the R-P phase which suggest the dilution limit on B-Site doping for Mo. Temperature dependent magnetization measurements exhibit ferromagnetic to paramagnetic transitions above the respective transition temperature (TC) of individual compounds. The parent compound displayed second order magnetic phase transition, while the first order transition was observed in the Mo-doped compositions. The maximum change in magnetic entropy (∆S<sub>M</sub><sup>max</sup>) values achieved for x = 0.0, 0.1, 0.2 and 0.3 samples are 2.98 J/kgK, 2.71 J/kgK, 2.64 J/kgK, 2.37 J/kgK respectively at 2.5 T applied field. Among the doped samples highest ∆S<sub>M</sub><sup>max</sup> value was achieved for x = 0.1 sample. For the these compounds the relative cooling power (RCP) slightly increased to 102 J/kg for x = 0.1 sample compared to the parent compound 98 J/kg. RCP values decreased for high Mo-concentrations and reached a lowest value 68 J/kg for x = 0.3 sample. Sufficient structural analysis carried out here suggest that the tetragonal symmetry in the B-site doped bilayer manganites reduced to simple perovskite symmetry above the dilution limit (x ≥ 0.2) thereby rigorously affecting the magnetic and magnetocaloric properties.
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Akshay Kumar,Kavita Kumari,Minji Shin,Seok Hwan Huh,Bon Heun Koo 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
In this work, the Simultaneous doping on A and B sites were performed in La1.2Ce0.2Ca1.6Mn1.9Cr0.1O7 (LCCMCO) compound to analyze the influence of Cerium (Ce) and Chromium (Cr) on the structural, magnetic and magnetocaloric properties. The bulk ceramics were prepared through solid-state sintering method by sequentially monitoring the heating episodes. The samples crystallized in tetragonal symmetry of double layer Ruddlesden-Popper phase. Parent compound (La1.4Ca1.6Mn₂O7) acquired pure phase while the co-doped sample has a mixed cubic perovskite phase. The samples possess well-connected microstructure with clearly defined grain boundaries. secondary oxide phases appeared at the surface of LCCMCO. The temperature dependent magnetization revealed ferromagnetic state of the compounds, meanwhile multiple magnetic transitions were observed in LCCMCO, which were ascribed to the magnetic clusters and/or due to the involvement of secondary phase. The ferromagnetic-paramagnetic transition temperature (Tc) was reduced from a value of 275 K for the parent compound to 235 K for LCCMCO. In general, Arrott plots disclosed second order phase transition for both samples, while the spin-clusters clearly revealed for LCMCO sample throughout the transition. The maximum magnetic entropy change (ΔSM) at 2.5 T was 3.02 J/kgK for LCMO and 2.48 for LCCMCO sample. The relative cooling power (RCP) enhanced from 98 J/kg to 109 J/kg at an applied field of 2.5 T respectively for parent and LCCMCO compound.
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Aljawfi, Rezq Naji,Kumari, Kavita,Vij, Ankush,Hashim, Mohd.,Chae, K. H.,Alvi, P. A.,Kumar, Shalendra Springer-Verlag 2018 Journal of materials science Materials in electron Vol.29 No.7
<P>In this study, Ti0.95Mn0.05O2-delta nanostructured thin films were fabricated by pulsed laser deposition technique followed by rapid thermal annealing (RTA) in pure O-2 and N-2 atmospheres. The RTA process induced a substantial change in the surfaces morphology and local atomic structure around Ti4+ cation that have been studied by means of atomic force microscopy, Raman scattering and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Raman spectra of the films were resembled to that of TiO2 rutile phase, and the change in the width of E-g (434 cm(-1)) Raman active modes has been attributed to oxygen non-stoichiometry. NEXAFS spectra were carried out in synchrotron facility at Ti/Mn L (3,2) edges and O-K edge. The ligand-field splitting, estimated from the energy difference between t(2g) and e(g) features in O K-edge spectra were similar to 2.81 eV for pristine and annealed film, which is a characteristic of the TiO2 rutile structure, and the asymmetry of t(2g) and e(g) bands at the O-K edge has been ascribed to oxygen vacancy (Vo(2+)). The annealing of film in O-2 gas optimized the surface structure and healed the Vo(2+) bridging, while the RTA in N-2 gas introduced Vo and reduced the valence state of Ti4+ (TiO2) into Ti3+ (Ti2O3) that have been probed by comparing the NEXAFS spectra of N-2 annealed film with the reference spectra of Ti2O3. Experimental and atomic multiplet calculations revealed that the Mn ions exist in 2+ valence state.</P>
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