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Öğe Static and dynamic properties of two-sublattice spin-crossover systems(Elsevier B.V., 2022) Yalçın, Orhan; Veliu, Valon; Özüm, Songül; Erdem, RızaWe 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 , 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 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 and using different temperature values. Finally, the flow diagram of the order parameters is depicted for different values of rate constant 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.Öğe Phenomenological Dynamics of Ising Magnets in the Presence of Magnetic Field: Widom Lines Captured from Slow Relaxation Time(2021) Özüm, SongülA complete phenomenological description for the relaxation dynamics of the Ising ferromagnets in the presence of external magnetic field h is given by using the pair approximation. To study the relaxation dynamics, we calculate two characteristic times (denoted as ?S, ?F ) using the rate constants which satisfy the Onsager reciprocity theorem. Temperature/magnetic field variations of ?S and ?F are investigated. We have shown that the extrema of the curves obtained for ?S when h 6= 0 determine the loci of correlation length maxima or the Widom lines. The results are compared with those of response functions and thermodynamic curvature. We observe that they exactly match that for the magnetic susceptibility.Öğe Synthesis and investigation of small g-values for smart spinel ferrite nanoparticles(Elsevier Science Sa, 2021) Bayrakdar, Harun; Yalçın, Orhan; Özüm, Songül; Cengiz, UğurSmart spinel and hexagonal ferrite nanoparticles (NPs) have been fabricated by ethylenediaminetetraacetic acid (EDTA) and cetyltrimethylammonium bromide (CTAB) assisted hydrothermal route by using NaOH solution. Electron spin resonance (ESR) measurements of the spinel and hexagonal ferrite NPs have been performed by a high sensitive conventional x.band (similar to 9.5-9.8 GHz) spectrometer at room temperature (RT). The measured five small g-values by ESR spectra at RT may be relevant for quantum information processing. Quantum computing and relativistic quantum computing by two-level system (qubit) have been realized by spinel type NPs at RT. Temperature evolution of magnetic hysteresis loops, magnetization, coercivity (H-C), saturation field (H-S), saturation magnetization (M-S) and remanent magnetization (M-r) have been investigated. (C) 2021 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) Özüm, Songül; Kavlak, Ramazan; Erdem, Rıza; Yalçın, OrhanThe 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) Yalçın, Orhan; Bayrakdar, Harun; Özüm, SongülSpinel 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 Hysteretic dipolar and quadrupolar properties of the spin-1 Blume-Emery-Griffiths model under pair approximation(World Scientific, 2021) Özüm, Songül; Erdem, Rıza; Yalçın, Orhan; Görgülüer, ÖmerAs a continuation of previously published work [A. Erdinç and M. Keskin, Int. J. Mod. Phys. B 18, 1603 (2004), doi:10.1142/S0217979204024823] the hysteretic properties of magnetization (m) and quadrupolar moment (q) have been investigated for the spin-1 Blume-Emery-Griffiths model using pair approximation. The magnetic field (h) dependence of m is produced for different values of the lattice coordination number (z), biquadratic interaction (k) and single-ion anisotropy (d). The (m,h) loops show different and novelty properties when d < 0. We also observed the hysteresis cycles in the (q,d), (q,h) and (m,d) planes. These curves strongly depend on biquadratic interaction k. Our results are found to be in good agreement with the other theoretical findings. © 2021 World Scientific Publishing Company.Öğe Hysteretic behavior of quadrupolar ordering in a 2D magnetic spin?1 Ising nanoparticle(Physical Society of the Republic of China, 2021) Erdem, Rıza; Yalçın, Orhan; Özüm, Songül; Şahin, Ayşe; Demirer, NazlıPair approximation technique has been used to study the quadrupolar ordering properties for the 2D magnetic spin-1 Ising nanoparticles, consisting of core and surface parts with an interface coupling. Similar to the magnetic hysteresis, it has been shown that the quadrupole order parameter (Q) as a function of single-ion anisotropy (D) has a ‘hysteresis’ character which is generally called quadrupole (or QD) hysteresis. The observed QD loops strongly depend on temperature (T), external magnetic field (H) and biquadratic exchange interaction (K). Shifted QD loops with an asymmetry are found when H and K values are increased. These behaviors are also discussed in relation to other theoretical findings.Öğe On the loci of relaxation time and magnetic dispersion maxima in the Mean-Field Ising model(Sakarya University Journal of Science SAUJS, 2020) Özüm, SongülBased on the phenomenological approach, loci of relaxation time and magnetic dispersion maxima near the critical regime in a spin-1/2 mean-field Ising model were performed. The shift in temperature (T) of relaxation time (?) maximum was detected and its behavior near the secondorder transition points are presented at different magnetic field values (h) and different lattice coordination numbers (q). An expression for the dynamic (or complex) susceptibility (? = ?1 - i?2) is also derived. The temperature dependence of the magnetic dispersion (?1) and magnetic absorption (?2) factors have been studied near the critical regime. It is found that the maximum of ?1 as a function of frequency (?) and kinetic coefficient (L) obeying an approximately exponential increases and decreases in T- ? and T-L planes near the critical regionÖğe Determination of the steady-state kinetics in a spin-1 Ising model using path probability method(World Scientific Publ Co PTE Ltd, 2020) Özüm, Songül; Erdem, RızaAs a continuation of our previously published work, we propose a theoretical framework for the determination of steady-state kinetics in a spin-1 Ising model by the path probability method. The framework is based on the principles of non-equilibrium statistical physics and is quite different from the phenomenological approach. We construct a set of linear kinetic equations for the order parameters using the non-linear dynamic (or rate) equations in the presence of external magnetic field. From the steady-state solutions of the linear equations, an expression for the complex (or dynamic) magnetic susceptibility (chi = chi(1) - i chi(2)) is derived. The temperature dependence of the magnetic dispersion relation (chi(1)) and magnetic absorption factor (chi(2)) has been studied in the ferromagnetic (FM) and paramagnetic (PM) phases as well as near the critical regime.Öğe Relaxation times obtained from the rate equations using path probability method for the spin-1 Ising model(World Scientific Publishing Co. Pte Ltd, 2019) Erdem, Rıza; Özüm, SongülWe have presented the time-dependent behaviors of a spin-1 Ising model (with both bilinear and biquadratic interactions) in the neighborhood of the equilibrium states via the path probability method. The rate equations as introduced by Keskin and co-workers (1989) have been linearized to obtain the characteristic relaxation times. The temperature variations of these times were produced in accordance with the Tanaka and Mannari's work (1976) on the equilibrium properties. Results are compared to one using Onsager's phenomenological theory and a good agreement is achieved. © 2019 World Scientific Publishing Company
