Papers by Keyword: Magnetism

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Authors: Jun Ming Li, Jian Li, Long Long Chen, Xiao Min Gong, Hong Mao
Abstract: During the synthesis of γ-Fe2O3 nanoparticles using a chemically-induced transition in a FeCl2 solution, Co-surface modification was attempted by adding Co (NO3)2 and NaOH to the solution. The magnetization behaviors, morphologies, crystal structure, and chemical compositions of the as-prepared samples were characterized using vibrating sample magnetometry, transmission electron microscopy, X-ray diffractometry, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The as-prepared particles consisted of γ-Fe2O3/CoFe2O4 composite crystallite and a CoCl2·6H2O coating. The molar, mass and volume ratios of the phases were estimated from the characterization results for each sample. The Co-modified γ-Fe2O3 nanoparticles’ anisotropic constant is approximately 1.48×10-1 J/cm3. Their coercivity depends on the size of composite crystallites, which is based on the γ-Fe2O3/CoFe2O4 content rather than the Co content.
Authors: Raminder Gill, P. Singh
Abstract: In the age of technology, with smaller and smaller electronic components being used in a growing number of applications, one pertinent application of mathematics and physics is the study of superconductivity. Superconductive materials are capable of conducting electricity without any resistance and were first discovered by Kamerlingh Onnes in 1911 in a compound He at 4.2 K in what was to prove to be one of the most significant scientific breakthroughs of the 20th Century. Superconductivity and Magnetism are mutually exclusive to each other but the coexistence of both the phenomena leads to very interesting research of superconductivity at room temperature. In this paper, we have studied the effect of ferromagnetic and antiferromagnetic interactions on the superconducting transition temperature.
Authors: Mario Cuoco, Paola Gentile, Marcello Gombos, Antonio Vecchione, Canio Noce
Abstract: The layered ruthenocuprate materials RuSr2LnCu2O8 and RuSr2(Ln1+xCe1-x)Cu2O10, with Ln=lanthanide or Y for both structures, consist of pairs of CuO2 planes alternating with perovskite-like sheets of vertex sharing RuO6 octahedra. Samples of Ru-1212 and Ru-1222 materials were known to show both superconducting and magnetic transitions. Here, we discuss the problem of the coexistence, considering a model which includes two types of carriers responsible separately for the ordered phases. By considering the interplay between a hybridization mechanism and the direct exchange coupling between these carriers, we look at the stability of the coexisting phase assuming an inhomogeneous superconducting phase.
Authors: S. Spagna, A. Wilson, M.B. Simmonds, J. Diederichs, R.E. Sager
Authors: De Hui Sun, De Xin Sun, Yu Hao
Abstract: Magnetic iron oxide nanomaterials (e.g. Fe3O4 and γ-Fe2O3) with different morphologies have aroused extensive attention due to their fundamental research and potential technological applications such as magnetic recording media, magnetic fluids and magnetic drug-targeting. In this article Fe3O4 nanosheets were successfully synthesized using triblock copolymer (PEO)20(PPO)70(PEO)20 (P123) micelles as structure-directing agents in the presence of surfactant-assisted ethylene glycol (EG) and precipitator hexamethylenetetramine (HMTA) at 70 °C for 2 h in N2. The Fe3O4 nanosheets have irregular shape with thickness of the Fe3O4 nanosheets about 10-15 nm. The X-ray diffraction (XRD) pattern confirms the Fe3O4 nanosheets have magnetite structure and its nine distinguishable diffraction peaks can be perfectly indexed to the (111), (220), (311), (222), (400), (422), (511), (440), and (533) planes of the fcc structure of magnetite. Its saturation magnetization (σs) is 58.4 emu/g. The possible formation mechanism of the Fe3O4 nanosheets in present work is proposed.
Authors: Oleg I. Gorbatov, Pavel A. Korzhavyi, Andrei V. Ruban, Yuri N. Gornostyrev
Abstract: Vacancy-solute interactions play a crucial role in diffusion-controlled phase transformations, such as ordering or decomposition, which occur in alloys under heat treatment or under irradiation. The knowledge of these interactions is important for predicting long-term behavior of nuclear materials (such as reactor steels and nuclear-waste containers) under irradiation, as well as for advancing our general understanding of kinetic processes in alloys. Using first-principles calculations based on density functional theory and employing the locally self-consistent Green’s function technique, we develop a database of vacancy-solute interactions in dilute alloys of bcc Fe with 3p (Al, Si, P, S), 3d (Ti – Cu), and 4d (Nb – Ag) elements. Interactions within the first two coordination shells have been computed in the ferromagnetic state as well as in the paramagnetic (disordered local moment) state of the iron matrix. Magnetism is found to have a very strong effect on the vacancy-solute interactions.
Authors: Tatyana N. Gnitetskaya, Elena V. Karnauhova
Abstract: A qualitative proof of diamagnetic non-zero magnetization based on the electromagnetic induction law is presented in this paper. Modeling diamagnetic phenomena as a result of Larmor precession or effect of the electromagnetic induction’s law in scale of one hydrogen-like atom performed in classical physics contributes to formation of obviously incorrect idea of the diamagnetic magnetization process in students. It is well-known that the average magnetic moment of a diamagnetic calculated with the help of classical statistics laws is zero which can be explained by quantum character of magnetic phenomena. On the contrary, electromagnetic induction’s law is effective both in classical and quantum physics. Applying it to the diamagnetism problem will allow to solve it for the diamagnetic in whole and to avoid averaging which is proved in the present paper.
Authors: Yang Wang, De Xiang Fu, Wen Zhi Li, Jian Hua Wang, Wen Hao Zhang, Yong Tao Li, Sheng Li Liu, Liang Xie, Hong Guang Zhang
Abstract: We studied the effect of annealing and Co ion doping on the structure, leakage current, ferroelectric polarization and magnetism of BiFeO3 samples. X-ray diffraction patterns demonstrate that an appropriate Co doping concentration is favor of suppressing the secondary phase but annealing treatment is apt to the growth of both the main and the secondary phases. The current density as a function of an electric field indicates that Co doping increases the leakage current density as samples before annealing but suppresses it after annealing. Annealing treatment improves the leakage for Co-doped sample and reduces it for the undoped sample. Ferroelectric hysteresis loops reflect that Co ions doping is liable to increase the ferroelectric polarization, while the sample is annealed it will do opposite effect. However the annealing treatment do improve the ferroelectricity for pure BiFeO3 sample. The magnetic hysteresis at room temperature shows the obvious enhancement of ferromagnetic properties with the sample after annealing.
Authors: A.P. Srivastava, Dinesh Srivastava, K.G. Suresh, G.K. Dey
Abstract: Microstructure and magnetic properties of a nanocrystalline soft magnetic material having composition Co64.5 Fe3.5 Si16.5 B13 Ni1.5 Cu1 has been studied. Amorphous ribbon could be produced by melt spinning unit. DSC analysis showed four distinct crystallization events. Heat treated samples were characterized using XRD and TEM techniques. Co2B, and CoB phases were found to crystallize before magnetic phase a−Co. Addition of copper was proved to have adverse effect on soft magnetic properties.
Authors: Oleg I. Gorbatov, Yuri N. Gornostyrev, Andrey R. Kuznetsov, Andrei V. Ruban
Abstract: Short-range order formation in dilute Fe-Si and Fe-Al alloys has been investigated by statistical Monte Carlo simulations with effective interactions deduced from first principles calculations for different magnetic structures of bcc Fe. We find that the variation of the magnetic order from ferromagnetic to paramagnetic leads to significant changes in effective cluster interactions and, as follow, in short-range order parameters of alloys. It is shown in agreement with experiment the B2 type short-range order is formed above the Curie temperature, TC, while the D03 type short-range order is preferred below TC.
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