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Structural and Magnetic Properties of Gd-Ni-co-doped BiFeO₃ Nanoparticles
Sandeep Kumar Singh Patel,Jae-Hyeok Lee,Min-Kwan Kim,Sang-Koog Kim 한국자기학회 2019 Journal of Magnetics Vol.24 No.3
Single-phase (GdNi)x(BiFe)1-x O₃ (x = 0, 0.025, and 0.05) nanoparticles of 30-40 nm particle size on average were fabricated using a sol-gel method. Transmission electron microscopy, X-ray diffraction as well as Raman spectral measurements and analyses revealed that the (GdNi)x(BiFe)1-xO₃ nanoparticles undergo a structural transformation from the rhombohedral R3c structure (for x = 0 and 0.025) to the triclinic P1 (for x = 0.05). X-ray photoemission spectroscopy served to confirm that co-doping of Gd<SUP>3+</SUP> and Ni<SUP>2+</SUP> ions decreases oxygen-vacancy concentration, reflecting less Fe<SUP>2+</SUP> content in the co-doped samples compared with pure BiFeO₃. Magnetization hysteresis loops showed that the magnetization value for x = 0.05 at 50 kOe increases significantly to M = 5.32 emu/g at 300 K and to 14.47 emu/g at 5 K, representing 760 and 690 % enhancements relative to those for x = 0. Fitting of the Curie-Weiss law to the observed magnetization-versus-temperature curves indicated the presence of weak ferromagnetic coupling in the samples. We also noted the exchange bias effect in the nano-size particles, possibly originating from exchange coupling between surface spins of an uncompensated ferromagnetic nature and core spins of an antiferromagnetic nature. We ascribed these significant improvements in the Gd-Ni-co-doped BiFeO₃ nanoparticles’ magnetic properties to the rhombohedral R3c to triclinic P1 structural transformation, due to the samples’ particle size being smaller than the modulation length of the canted antiferromagnetic ordering of the Fe<SUP>3+</SUP> spins. These enhanced magnetic properties, notably, might prove useful for a variety of spintronic applications.
Sandeep Chaudhary, Kashyap Arvindbhai Patel, 김두기(Dookie Kim),조성국(Sung Gook Cho),Ahmer Ali 한국구조물진단유지관리학회 2011 한국구조물진단학회 학술발표회논문집 Vol.15 No.1
Studies are presented for the dynamic behaviour of steel-concrete composite floors. A typical two spans composite floor is considered for this study and assumed to be subjected to a typical earthquake. The deflection and stresses are obtained at different time instants for the composite floor with rigid connection and flexible connection. The FE model developed, in ABAQUS, for the study accounts for the nonlinear material behaviour. The flexibility of shear connectors between steel girder and concrete slab is found to significantly affect the dynamic behaviour of steel-concrete composite floors.
Patel, Sandeep Kumar Singh,Lee, Jae-Hyeok,Bhoi, Biswanath,Lim, Jung Tae,Kim, Chul Sung,Kim, Sang-Koog Elsevier 2018 Journal of magnetism and magnetic materials Vol.452 No.-
<P><B>Abstract</B></P> <P>We fabricated Gd-doped Y<SUB>3</SUB>Fe<SUB>5</SUB>O<SUB>12</SUB> (YIG) nanoparticles by a modified sol–gel method. We investigated the effects of isovalent Gd<SUP>3+</SUP>-ion substitution on the structural and magnetic properties of Y<SUB>3−x</SUB>Gd<SUB>x</SUB>Fe<SUB>5</SUB>O<SUB>12</SUB> (0 ≤ x ≤ 3) nanoparticles. Isovalent Gd<SUP>3+</SUP>-ion substitution for Y<SUP>3+</SUP> leads to lattice expansion and change in the Fe(<I>a</I>)–O–Fe(<I>d</I>) bond angle. The X-ray photoemission spectroscopy and Mössbauer measurements revealed a high-spin state of Fe<SUP>3+</SUP>. The Mössbauer analysis showed an increase in the Fe<SUB>(d)</SUB> <SUP>3+</SUP>/Fe<SUB>(a)</SUB> <SUP>3+</SUP> ratio, indicating a relocation of Y<SUP>3+</SUP> ions at the dodecahedral sites and Fe<SUP>3+</SUP> ions at the octahedral sites. The magnetic properties could be explained in terms of magnetic-structural evolution with increasing Gd<SUP>3+</SUP> content. The field dependence of magnetization indicated a clear decrease of the magnetization while the magnetic anisotropy first decreases and then increases with the increase of Gd<SUP>3+</SUP> content. These Gd<SUP>3+</SUP>-ion-substituted nanocrystalline garnet ferrites are suitable for use in a variety of magneto-optical applications.</P>
Patel, Sandeep Kumar Singh,Lee, Jae-Hyeok,Kim, Min-Kwan,Bhoi, Biswanath,Kim, Sang-Koog The Royal Society of Chemistry 2018 Journal of Materials Chemistry C Vol.6 No.3
<P>We fabricated single-crystalline, Gd-doped BiFeO3 (BFO) nanowires using a hydrothermal technique. X-ray diffraction (XRD) data combined with their Rietveld refinements and high-resolution transmission electron microscopy (HRTEM) revealed pure single-phase crystalline Bi1−xGdxFeO3 (<I>x</I> = 0, 0.05, 0.10) nanowires of 40-60 nm diameter and their structural transformation from the rhombohedral <I>R</I>3<I>c</I> (for <I>x</I> = 0 and 0.05) to the orthorhombic <I>Pn</I>21<I>a</I> crystal structure (for <I>x</I> = 0.10). The addition of Gd<SUP>3+</SUP> ions to the pure-phase BFO leads to remarkable changes in the structural and magnetic properties, and these effects are caused by differences in the ionic-radii and magnetic moment between the Bi<SUP>3+</SUP> and Gd<SUP>3+</SUP> ions. According to the observed magnetization-field (<I>M-H</I>) and magnetization-temperature (<I>M</I>-<I>T</I>) curves, with increasing Gd<SUP>3+</SUP> concentration, the saturation magnetization (<I>M</I>S), squareness (<I>M</I>r/<I>M</I>S), coercivity (<I>H</I>C), exchange-bias field (<I>H</I>EB) and magnetocrystalline anisotropy (<I>K</I>) increased markedly, by <I>M</I>S = 1.26 emu g<SUP>−1</SUP> (640%), <I>M</I>r/<I>M</I>S = 0.19 (20.5%), <I>H</I>C = 7788 Oe (4560%), <I>H</I>EB = 501 Oe (880%) and <I>K</I> = 1.62 × 10<SUP>5</SUP> erg cm<SUP>−3</SUP> (3500%), for <I>x</I> = 0.10 relative to the data for <I>x</I> = 0. In such Gd-doped BFO nanowire samples, spin-canted Dzyaloshinskii-Moriya interaction, remarkable enhancements in the magnetocrystalline anisotropy as well as uncompensated surface ferromagnetic spin states in the antiferromagnetic core regions were also found. Such remarkable enhancements in Gd-doped BFO nanowires might offer a variety of spintronic applications.</P>
Transarterial Radioembolization Agents: a Review of the Radionuclide Agents and the Carriers
Alrfooh Aysheh,Patel Aditi,Laroia Sandeep 대한핵의학회 2021 핵의학 분자영상 Vol.55 No.4
Liver tumors, both primary and secondary to metastatic disease, remain a major challenge, with an increasing incidence. In this context, taking advantage of the dual blood supply of the liver, and the fact that liver tumors derive majority of their blood supply from the hepatic artery, intraarterial therapies are gaining popularity. Intraarterial liver-directed therapy (IALDT) is the option when the surgery is not feasible due to the number of metastases or for other reasons. Transarterial radioembolization (TARE) is a specific type of IALDT, where a carrier particle/microsphere is labeled with a radioactive substance and then is injected into hepatic artery for therapeutic purposes. As this field is rapidly evolving, with multiple agents being investigated and being introduced into clinical practice, it is hard for the practitioners and researchers to encompass all the available information concisely. This article aims to present a comprehensive review of the prominent TARE technologies.
A tension stiffening model for analysis of RC flexural members under service load
K. A. Patel,Sandeep Chaudhary,A.K. Nagpal 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.17 No.1
Tension-stiffening is the contribution of concrete between the cracks to carry tensile stresses after cracking in Reinforced Concrete (RC) members. In this paper, a tension-stiffening model has been proposed for computationally efficient nonlinear analysis of RC flexural members subjected to service load. The proposed model has been embedded in a typical cracked span length beam element. The element is visualized to consist of at the most five zones (cracked or uncracked). Closed form expressions for flexibility and stiffness coefficients and end displacements have been obtained for the cracked span length beam element. Further, for use in everyday design, a hybrid analytical-numerical procedure has been developed for nonlinear analysis of RC flexural members using the proposed tension-stiffening model. The procedure yields deflections as well as redistributed bending moments. The proposed model (and developed procedure) has been validated by the comparison with experimental results reported elsewhere and also by comparison with the Finite Element Method (FEM) results. The procedure would lead to drastic reduction in computational time in case of large RC structures.