Yazar "Ozum, S." seçeneğine göre listele
Listeleniyor 1 - 5 / 5
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Comparison effects and electron spin resonance studies of alpha-Fe2O4 spinel type ferrite nanoparticles(PERGAMON-ELSEVIER SCIENCE LTD, 2014) Bayrakdar, H.; Yalcin, O.; Cengiz, U.; Ozum, S.; Anigi, E.; Topel, O.alpha-Fe2O4 spinel type ferrite nanoparticles have been synthesized by cetyltrimethylammonium bromide (CTAB) and ethylenediaminetetraacetic acid (EDTA) assisted hydrothermal route by using NaOH solution. Electron spin resonance (ESR/EPR) measurements of alpha-Fe2O4 nanoparticles have been performed by a conventional x-band spectrometer at room temperature. The comparison effect of nanoparticles prepared by using CTAB and EDTA in different alpha-doping on the structural and morphological properties have been investigated in detail. The effect of EDTA-assisted synthesis for alpha-Fe2O4 nanoparticles are refined, and thus the spectroscopic g-factor are detected by using ESR signals. These samples can be considered as great benefits for magnetic recording media, electromagnetic and drug delivery applications. (C) 2014 Elsevier B.V. All rights reserved.Öğe Martensitic and austenitic transformations in core-surface cubic nanoparticles(ELSEVIER SCIENCE BV, 2015) Ozum, S.; Yalcin, O.; Erdem, R.; Bayrakdar, H.; Eker, H. N.As a continuation of our recently published work, we have used the pair approximation in Kikuchi version to investigate martensitic and austenitic transformations in homogeneous (HM) and composite (CM) cubic nanoparticles (CNPs) based on the Blume-Emery-Griffiths model. A single cubic nanoparticle made of a core surrounded by a surface is considered as shaped in two dimensional (2D) square arrays instead of hexagonal array. From the phase diagrams of HM and CM-CNPs it has been observed that the martensitic-austenitic transformations (MT-AT) occurred. The influence of the exchange coupling and single-ion anisotropy parameters in the model Hamiltonian on the MT-AT is studied and analyzed in comparison with the results for hexagonal nanoparticles. Significant changes of the phase transition points and hysteresis behaviours depending upon the particle structure have been discussed. (C) 2014 Elsevier B.V. All rights reserved.Öğe Nanosized Monolayer on Square Lattice within Spin-1 Ising Model: Hysteretic Properties with Odd Interactions(Polish Acad Sciences Inst Physics, 2021) Ozum, S.; Kavlak, R.; Erdem, R.; Yalcin, O.The hysteretic properties of a nanosized monolayer on the square lattice have been studied based on the spin-1 Ising model, including a single-ion anisotropy (D) and dipolar-quadrupolar (or odd, L) interaction parameters using the pair approximation. The nanosized monolayer is divided into the core, core-surface, and surface parts as introduced in J. Mugn. Magn. Mater. 373, 217 (2015). The dipolar (or magnetization M) and quadrupolar (Q) order parameters are calculated. We have investigated M vs. magnetic field H behaviors for different values of L, temperatures T, and monolayer sizes R. We also observed Q-D, M-D and Q-H hysteresis loops. These results are discussed in relation to other theoretical findings.Öğe Origin of Cross-Over Phenomenon of Hysteresis Loops and High Absorption Loss Properties for Spinel Ferrite Nanoparticles(Polish Acad Sciences Inst Physics, 2021) Yalcin, O.; Bayrakdar, H.; Ozum, S.Spinel ferrite nanoparticles have been synthesized by the surfactant-assisted hydrothermal route using cetyltrimethylammonium bromide (CTAB) and ethylenediaminetetraacetic acid (EDTA) in the NaOH solution. Temperature evolution of magnetic hysteresis loops has been investigated in detail. The magnetic characterization of spinel nanoparticles has been measured by a quantum design vibrating sample magnetometer model 6000. The origin of a cross-over feature of ferrite nanoparticles has been observed at room temperature. Microwave properties of ferrites were investigated with the use of an Anritsu MS2028C VNA Master. The present studies also demonstrate that a microwave absorber can be fabricated within a ferrite polymer nanocomposite for technological applications up to 16 GHz, with the reflection loss of more than -60 dB and -50 dB by using CTAB and EDTA, respectively.Öğe Static and dynamic properties of two-sublattice spin-crossover systems(Elsevier, 2022) Yalcin, O.; Veliu, V.; Ozum, S.; Erdem, R.We investigate the static and dynamic properties of spin-crossover systems in the presence of an external magnetic field using two-sublattice Ising-like Hamiltonian. At low temperatures both sublattices are in the LS state, and in the HS state at high temperatures. The new feature of spin-crossover is depicted for our model when we take the non-equivalent sublattices JA =/ JB, the two-step spin-crossover phase transition is obtained with the presence of the hysteresis loop. In order to study the properties of two-step spin-crossover, we use the lowest approximation of the cluster variation method for static properties. The dynamic properties of the system with bilinear interactions are studied by the path probability method. We present high-spin state fraction nHS vs temperature and magnetic field variations for constant values of the degeneracy ratio between high-spin and low -spin states. In the present model, we obtained the relaxation curves of the order parameters SA and SB using different temperature values. Finally, the flow diagram of the order parameters is depicted for different values of rate constant k1 and temperature, which displays the stable, metastable, and unstable properties. Static and dynamic self-consistent equations of the system were performed by using Newton-Raphson and Runge-Kutta methods.
