Yazar "Veliu, Valon" seçeneğine göre listele

Listeleniyor 1 - 3 / 3
  • [ X ]
    Öğe
    Ising-like model for the two-step spin-crossover systems: Static properties with magnetic field effects using cluster variation method
    (Institute of Molecular Physics, Polish Academy of Sciences Faculty of Physics, Adam Mickiewicz University, Pozna?, 2021) Veliu, Valon; Erdem, Rıza; Özüm, Songül; Yalçın, Orhan
    We investigate the static properties of a two?sublattice Ising?like Hamiltonian for spin-crossover (SCO) systems in the presence of an external magnetic field. Self?consistent equations are obtained using cluster variation method in the lowest approximation. From the solutions of these equations, we present high?spin state fraction vs. temperature and magnetic field variations for various values of the degeneracy ratio between high?spin and low?spin states (r). It is shown that two metastable and one unstable (or saddle) branches in the SCO region are displayed in the r > 1 case while the metastable states disappear and only one saddle point occurs when r = 1. However, only stable states are obtained at high temperatures outside the SCO region. The comparison of our results to other theoretical treatments is also given
  • [ X ]
    Öğe
    Static and dynamic properties of two-sublattice spin-crossover systems
    (Elsevier B.V., 2022) Yalçın, Orhan; Veliu, Valon; Özüm, Songül; Erdem, Rıza
    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 , 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.
  • [ X ]
    Öğe
    Static properties of spin-crossover with magnetic interaction of Spin-1 Blume-Emery-Griffiths model for two-sublattices
    (2022) Veliu, Valon; Özüm, Songül; Yalçın, Orhan; Erdem, Rıza
    The static properties of the spin-1 Blume-Emery-Griffiths (BEG) model for two-sublattices with the presence of an external magnetic field for spin-crossover (SCO) and magnetic ordering are presented. To study the static properties of SCO and magnetic ordering we use the cluster variation method in the lowest approximation (CVMLA). The obtained self-consistent equations are solved using the Newton Raphson method. From these solutions of the self-consistent equations, we present the thermal behaviors of the high-spin fraction (nHS = QA+QB 2 ) state and magnetizations (MF = MA+MB 2 ) for different values of magnetic interaction and quadrupolar interaction parameters. Also, the properties of SCO and magnetic ordering for varying external magnetic fields are presented. It is shown some properties that magnetization is zero and SCO exhibits a first-order phase transition when the temperature increases for different value of magnetic interaction and when temperature decreases both magnetization and SCO are exhibiting the first-order phase transition with the absence of the external magnetic. SCO is different when the temperature is decreasing. However, different states appear for magnetization and SCO with varying external magnetic field for fixed temperature. Our results were compared with other theoretical investigations also given.