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E. Albayrak

Publications and source records attributed to E. Albayrak.

6 recordsLinked to original sources

Critical, compensation and hysteresis behaviors studies in the ferrimagnetic Blume-Capel model with mixed half-integer spin-(3/2, 7/2): Exact recursion relations calculations

The exact recursion relations are used to study the mixed half-integer spin-(3/2, 7/2) Blume-Capel Ising ferrimagnetic system on the Bethe lattice. Ground-state phase diagrams are computed in the $({D_{A}}/{q|J|}, {D_{B}}/{q|J|})$ plane to reveal different possible ground states of the model. Using the thermal changes of the order-parameters, interesting temperature dependent phase diagrams are constructed in the ($D_{A}/|J|$, $kT/|J|$), ($D_{B}/|J|$, $kT/|J|$) planes as well as in the ($D/|J|$, $kT/|J|$) plane where $D=D_A=D_B$. It is revealed that the system exhibits first- and second-order phase transitions and compensation temperatures for specific model parameter values. Under the constraint of an external magnetic field, the model also produces multi-hysteresis behaviors as single, double and triple hysteresis cycles. Particularly, the impacts of the ferrimagnetic coupling $J$ on the remanent magnetization and the coercitive fields for selected values of the other physical parameters of the system are pointed out. Our numerical results are qualitatively consistent with those reported in the literature.

cond-mat.stat-mech

Hexagonal core-shell structure nanowire with high spins of spin-3/2 and spin-5/2

The magnetic properties and hysteresis loops for the hexagonal Ising nanowire (HIN) with a core-shell structure consisting of mixed spins with the core spin being spin-5/2 and the shell spins being spin-3/2 are studied. The Blume-Capel model is considered by using the mean-field approximation (MFA) based on the Gibbs--Bogoliubov inequality for free energy. The impact of different bilinear interaction parameters ($J_{cc}, J_{ss}, J_{cs}$) between the core, shell, and core and shell spins, respectively, including the crystal ($D_c, D_s$) and external magnetic fields ($h=h_c=h_s$) at the core and shell sites, are taken into consideration. In order to obtain phase diagrams on various planes, the thermal changes of the net, core, and shell magnetizations are investigated for various values of our system parameters. It is discovered that the model exhibits only second-order phase transitions when $h=0.0$ for $D$ greater or equal to zero, first- and second-order phase transitions for $h\neq0.0$ and compensation temperatures for all $h$.

cond-mat.stat-mech

Ferromagnetic Heisenberg model with the Dzyaloshinskii-Moriya interaction

The spin-1/2 Heisenberg model is formulated in terms of a mean-field approximation (MFA) by using the matrix forms of spin operators $\hat{S}_x,\hat{S}_y$ and $\hat{S}_z$ in three-dimensions. The considered Hamiltonian consists of bilinear exchange interaction parameters $(J_x,J_y,J_z)$, Dzyaloshinskii-Moriya interactions $(Δ_x,Δ_y,Δ_z)$ and external magnetic field components $(H_x,H_y,H_z)$. The magnetization and its components are obtained in the MFA with the general anisotropic case with $J_x\neq J_y \neq J_z$ for various values of coordination numbers $q$. Then, the thermal variations of magnetizations are investigated in detail to obtain the phase diagrams of the model for the isotropic case with $J_x=J_y=J_z>0$. It is found that the model exhibits ferromagnetic, paramagnetic, random phase regions and an extra ferromagnetic phase at which the components of magnetizations present branching.

cond-mat.stat-mech

Anisotropic Heisenberg model for the mixed spin-3/2 and spin-1/2 under random crystal field

Thermodynamic properties of the mixed spin-3/2 and spin-1/2 Heisenberg model are examined within the Oguchi approximation in the presence of a random crystal-field (RCF). The RCF is either introduced with probability p or turned off with probability 1-p randomly. The thermal variations of the global magnetization and free energy of the system are investigated to construct the phase diagrams for the classical, quantum and anisotropic cases. Different results revealed that no qualitative changes exist between them. Quantum effects are found to be present and abundant in the quantum model in the negative D -range. This phenomenon has a strong decreasing effect on the critical temperature which becomes much lower than in the classical case. In the presence of an external field, it was observed that coercivity and remanence decrease in a wide range of the absolute temperature.

cond-mat.soft

Phase diagrams and critical behaviours of the mixed spin-5/2 and spin-7/2 Ising system

We used mean-field theory based on the Bogoliubov inequality for the Gibbs free energy to examine the magnetic properties of a mixed spin-5/2 and spin-7/2 Blume-Capel ferrimagnetic system. The thermal behaviours of the system magnetization are classified according to the extended Néel nomenclature. The system exhibits compensation phenomena where a complete cancellation of sublattice magnetizations is observed below the critical temperature. Temperature-dependent phase diagrams are constructed for the case of unequal sublattice crystal field interactions. Under appropriate conditions, our calculations reveal first-order transitions in addition to second-order ones previously observed in Monte Carlo simulations.

cond-mat.stat-mech

Influence of steps on the tilting and adsorption dynamics of ordered Pn films on vicinal Ag(111) surfaces

Here we present a structural study of pentacene (Pn) thin films on vicinal Ag(111) surfaces by He atom diffraction measurements and density functional theory (DFT) calculations supplemented with van der Waals (vdW) interactions. Our He atom diffraction results suggest initial adsorption at the step edges evidenced by initial slow specular reflection intensity decay rate as a function of Pn deposition time. In parallel with the experimental findings, our DFT+vdW calculations predict the step edges as the most stable adsorption site on the surface. An isolated molecule adsorbs as tilted on the step edge with a binding energy of 1.4 eV. In addition, a complete monolayer (ML) with pentacenes flat on the terraces and tilted only at the step edges is found to be more stable than one with all lying flat or tilted molecules, which in turn influences multilayers. Hence our results suggest that step edges can trap Pn molecules and act as nucleation sites for the growth of ordered thin films with a crystal structure similar to that of bulk Pn.

cond-mat.str-el