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The mixed-spins 1/2 and 3/2 Blume-Capel model with a random crystal field

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Chinese Physics B 2012年第6期21卷 485-489页

作者： erhan albayrak Erciyes University Department of Physics38039KayseriTurkey

The random crystal field （RCF） effects are investigated on the phase diagrams of the mixed-spins 1/2 and 3/2 Blume-Capel （BC） model on the Bethe lattice. The bimodal random crystal field is assumed and the recursion relations are employed for the solution of the model. The system gives only the second-order phase transitions for all values of the crystal fields in the non-random bimodal distribution for given probability. The randomness does not change the order of the phase transitions for higher crystal field values, i.e., it is always second-order, but it may introduce first-order phase transitions at lower negative crystal field values for the probability in the range about 0.20 and 0.45, which is only the second-order for the non-random case in this range. Thus our work claims that randomness may be used to induce first-order phase transitions at lower negative crystal field values at lower probabilities.

关键词： randomness crystal field Bethe lattice mixed spin bimodal

Thermal entanglement in two-qutrit spin-1 anisotropic Heisenberg model with inhomogeneous magnetic field

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Chinese Physics B 2010年第9期19卷 183-190页

作者： erhan albayrak Erciyes University Department of Physics

The thermal entanglement of a two-qutrit spin-1 anisotropic Heisenberg XXZ chain in an inhomogeneous magnetic field is studied in detail. The effects of the external magnetic field （B）, a parameter b which controls the inhomogeneity of B, and the bilinear interaction parameters Jx = Jy ≠ Jz on the thermal variation of the negativity are studied in detail. It is found that negativity N decreases when the values of magnetic field, inhomogeneity b and temperature are increasing. In addition, N remains at higher temperatures for higher values of Jz and lower values of B and b.

关键词： negativity XXZ model thermal entanglement qutrit spin-1 magnetic field

The Mixed Spin-1/2 and Spin-1 Ising–Heisenberg Model in the Mean-Field Approximation: a New Approach

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Chinese Physics Letters 2018年第3期35卷 84-88页

作者： erhan albayrak Erciyes University Department of Physics

Thermodynamic properties of the mixed spin-1 and spin-1/2 Ising-Heisenberg model are studied on a honeycomb lattice using a new approach in the mean-field approximation to analyze the effects of longitudinal Dz and transverse Dx crystal fields. The phase diagrams are calculated in detail by studying the thermal variations of the order parameters, i.e., magnetizations and quadrupole moments, and compared with the literature to assess the reliability of the new approach. It is found that the model yields both second- and first-order phase transitions, and tricritical points. The compensation behavior of the model is also investigated for the sublattice magnetizations, and longitudinal and transverse quadrupolar moments. The latter type of compensation is observed in the literature but its possible importance is overlooked.

关键词： Heisenberg Model in the Mean-Field Approximation The Mixed Spin-1/2 and Spin-1 Ising a New Approach

Spin-1 Blume-Capel model with longitudinal random crystal and transverse magnetic fields:A mean-field approach

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Chinese Physics B 2013年第7期22卷 494-498页

作者： erhan albayrak Department of Physics Erciyes University

The spin-1 Blume–Capel model with transverse and longitudinal external magnetic fields h, in addition to a longitudinal random crystal field D, is studied in the mean-field approximation. It is assumed that the crystal field is either turned on with probability p or turned off with probability 1 p on the sites of a square lattice. Phase diagrams are then calculated on the reduced temperature crystal field planes for given values of γ=Ω/J and p at zero h. Thus, the effect of changing γ and p are illustrated on the phase diagrams in great detail and interesting results are observed.

关键词： random crystal field transverse field spin-1 Blume–Capel model

Thermal Entanglement in a Two-Qutrit Spin-1 Anisotropic Heisenberg Model

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Chinese Physics Letters 2011年第2期28卷 43-46页

作者： erhan albayrak Erciyes University Department of Physics38039KayseriTurkey

The negativity(N)as a measure of thermal entanglement(TE)is studied for a two-qutrit spin-1 anisotropic Heisenberg XXZ chain with Dzyaloshinskii-Moriya(DM)interaction in an inhomogeneous magnetic field in *** effects of the DM interaction parameter D_(z)on the thermal variation of the N for given values of the external magnetic Reid B,a parameter b which controls the inhomogeneity of B and the bilinear interaction parameters J_(x)=J_(y)≠J_(z)are *** is found that N persists to higher values and to higher temperatures for the higher values of±D_(Z)and for the higher positive values of J_(z),*** the antiferromagnetic(AFM)*** J_(z)<0,the ferromagnetic(FM)case,and D_(z)is small,and if J_(z)is strong enough to compete with D^(z),N *** addition,N declines with the increasing values of B and b.

关键词： Heisenberg interaction bilinear

Phase diagrams of the spin-2 Ising model in the presence of a quenched diluted crystal field distribution

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Chinese Physics B 2012年第11期21卷 114-120页

作者： Ali Yigit erhan albayrak ankiri Karatekin University Department of Physics Erciyes University Department of Physics

We have investigated the random crystal field effects on the phase diagrams of the spin-2 Blume-Capel model for a honeycomb lattice using the effective-field theory with correlations. To do so, the thermal variations of magnetization are studied via calculating the phase diagrams of the model. We have found that the model displays both second-order and first-order phase transitions in addition to the tricritical and isolated points. Reentrant behavior is also observed for some appropriate values of certain system parameters. Besides the usual ground-state phases of the spin-2 model including ±2, ~1, and 0, we have also observed the phases ±3/2 and ±1/2, which are unusual for the spin-2 case.

关键词： spin-2 model random crystal field effective-field theory isolated critical points andtriciritical points

Bond Dilution Effects on Bethe Lattice the Spin-1 Blume–Capel Model

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Communications in Theoretical Physics 2017年第9期67卷 361-365页

作者： erhan albayrak Erciyes University Department of Physics

The bond dilution effects are investigated for the spin-1 Blume-Capel model on the Bethe lattice by using the exact recursion relations. The bilinear interaction parameter is either turned on ferromagnetically with probability p or turned off with probability 1 - p between the nearest-neighbor spins. The thermal variations of the order-parameters are studied in detail to obtain the phase diagrams on the possible planes spanned by the temperature （T）, probability （p） and crystal field （D） for the coordination numbers q = 3, 4, and 6. The lines of the second-order phase transitions, To-lines, combined with the first-order ones, Tt-lines, at the tricritical points （TCP） are always found for any p and q on the （T, D）-planes. It is also found that the model gives only Tc-lines, To-lines combined with the Tt-lines at the TCP＇s and only Tt-lines with the consecutively decreasing values of D on the （T, p）-planes for aJ1 q.

关键词： bond dilution spin-l Bethe lattice bilinear interaction Blume-Capel

Phase diagrams of spin-3/2 Ising model in the presence of random crystal field within the effective field theory based on two approximations

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Chinese Physics B 2013年第10期22卷 186-191页

作者： Ali Yigit erhan albayrak Department of Physics anklrl Karatekin University Department of Physics Erciyes University

The bimodal random crystal field （A） effects are investigated on the phase diagrams of spin-3/2 Ising model by using the effective-field theory with correlations based on two approximations： the general van der Waerden identity and the approximated van der Waerden identity. In our approach, the crystal field is either turned on or turned off randomly for a given probability p or q = 1 -p, respectively. Then the phase diagrams are constructed on the （A,kT/J） and （p,kT/J） planes for given p and A, respectively, when the coordination number is z = 3. Furthermore, the effect of randomization of the crystal field is illustrated on the （△,kT/J） plane for p = 0.5 when z - 3,4, and 6. All these are carried out for both approximations and then the results are compared to point out the differences. In addition to the lines of second-order phase transitions, the model also exhibits first-order phase transitions and the lines of which terminate at the isolated critical points for high p values.

关键词： spin-3/2 random crystal field effective-field theory isolated critical point

Spin-3/2 Ising model AFM/AFM two-layer lattice with crystal field

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Chinese Physics B 2009年第10期18卷 4193-4207页

作者： erhan albayrak Ali Yigit Department of Physics Erciyes University

The spin-3/2 Ising model is investigated for the case of antiferromagnetic （AFM/AFM） interactions on the two- layer Bethe lattice by using the exact recursion relations in the pairwise approach for given coordination numbers q=3, 4 and 6 when the layers are under the influences of equal external magnetic and equal crystal fields. The ground state （GS） phase diagrams are obtained on the different planes in detail and then the temperature-dependent phase diagrams of the system are calculated accordingly. It is observed that the system presents both second- and first-order phase transitions for all q, therefore, tricritical points. It is also found that the system exhibits double-critical end points and isolated points. The model also presents two Neel temperatures, TN, and the existence of which leads to the reentrant behaviour.

关键词： Bethe lattice spin ground state AFM/AFM layer phase