Mixed-spin Model Research Articles

Magnetocaloric properties and hysteresis loops of hexagons in a square–hexagon-octagon (4-6-8) structure with mixed spins: Monte Carlo study

In this work, we have studied the magnetocaloric properties of a 1, 3/2 and 5/2 mixed spin model on a square–hexagon-octagon (4-6-8) structure, investigated by Monte Carlo simulations. The total magnetization and the magnetization of each sub-lattice of the mixed-spin lattice have been analyzed. We investigated the effects of the external magnetic field, the exchange coupling interactions and the temperature in order to explicit the magnetic properties of these structure systems. The magnetic susceptibility and heat specific were determined. The magnetic spin-reorientation transition and ferrimagnetic-paramagnetic transitions were found, along with the magnetic entropy changes. Finally, the hysteresis loops under the effect of exchange interactions, temperatures and the crystal fields have been discussed.

Dynamic hysteresis features of a mixed spin (1/2, 3/2) Ising system within the path probability method

ABSTRACT The dynamic hysteresis features (DHFs) of a mixed spin (1/2, 3/2) model on a square lattice was studied within the path probability method (PPM) in the presence of a time-varying (sinusoidal) magnetic field. The PPM contains three rate constants in which one of them (k 2) may be considered as corresponding to the wheel speed in the melt-spinning method (MSM). Influences of the temperature (T), angular frequency (ω), and the rate constant (k2 ) on the DHFs for the attractive bilinear interaction were examined. We also investigated the magnetic coercive fields and remanent magnetizations as functions T, ω, and k 2. Some of our obtained results are in qualitatively good agreement with some theoretical studies, experimental reported works on some magnetic materials, and the hysteresis loops obtained by using the MSM.

Instance Independence of Single Layer Quantum Approximate Optimization Algorithm on Mixed-Spin Models at Infinite Size

This paper studies the application of the Quantum Approximate Optimization Algorithm (QAOA) to spin-glass models with random multi-body couplings in the limit of a large number of spins. We show that for such mixed-spin models the performance of depth 1 QAOA is independent of the specific instance in the limit of infinite sized systems and we give an explicit formula for the expected performance. We also give explicit expressions for the higher moments of the expected energy, thereby proving that the expected performance of QAOA concentrates.

Ab-initio calculations combined with Monte Carlo simulation of the physical properties of Fe3S4 compound

The main objective of this paper is to evaluate the physical properties of Fe 3 S 4 material. To do so, Ab-initio calculations and Monte Carlo Simulations (MCS) by means of the mixed spin model have been used. Fe 3 S 4 compound is formed by two magnetic sub-lattices, one occupied the A tetrahedral with spin 5/2 and the other occupied by B octahedral with both spin 2 and 5/2. The density of states (DOS) has been investigated and confirmed that the compoundis a half metal. Further, the magnetization, susceptibility and specific heat curves have been determined for different sizes of the systemand fromwhich the values of critical exponentsand the critical temperature (T c ) have been calculated. Besides, the temperature-dependent magnetization for different values of crystal field has been analyzed to provide an insight into the relation compensation phenomena and crystal field effect.

Mixed Spin‐(3/2,7/2) Ising‐Type Ferrimagnet: Monte Carlo–Mean Field Treatment

Mean field and Monte Carlo simulations techniques are applied to study the behavior of a mixed Ising spin model in a square lattice where spins 7/2 are located in alternating sites with spins 3/2. There is an antiferromagnetic interaction between nearest neighbors, ferromagnetic interactions between next‐nearest neighbors, crystal fields, and a magnetic external field. The role of the different interactions in the magnetic behavior of the system is explored. It is found that depending on the combination of parameters in the Hamiltonian this system presents multiple hysteresis loops, exchange bias, compensation temperatures, and discontinuous magnetizations. The results are compared with previous studies that do not include the ferromagnetic next‐nearest neighbor interactions and found that they can have a strong effect in the magnetic behavior of the system.

Entropic uncertainty relation of a qubit–qutrit Heisenberg spin model and its steering

We investigate the quantum-memory-assisted entropic uncertainty relation (QMA-EUR) in a Heisenberg XYZ mixed-spin (1/2, 1) model. Coupling strength, Dzyaloshinskii–Moriya (DM) interaction and inhomogeneous magnetic field, respectively, contributing to QMA-EUR by a thermal entanglement in the hybrid-spin model are studied in detail. Furthermore, we compare the uncertainty of the bipartite hybrid model with those of qubit–qubit and qutrit–qutrit systems. Meanwhile, the effects of local PT-symmetric operation and weak measurement on the steering of entropic uncertainty are analyzed. We find that the local PT-symmetric operation can reduce the entropic uncertainty, and the entropic uncertainty can also be decreased by weak measurement reversal.

Dynamic magnetic hysteresis loop features of molecular-based magnetic materials and ferrimagnetic systems by the path probability method

Dynamic magnetic hysteresis loops (DMHL) features of molecular-based magnetic materials and ferrimagnetic systems are investigated by a mixed spin (1/2, 1) model by means of the path probability method (PPM). The PPM contains two rate constants; hence the DMHL features have been studied by using the method with two rate constants. In particular, the effects of the repulsive (J<0) and attractive (J>0) bilinear nearest-neighbor pair interactions, temperature (T), crystal-field interaction (D), angular frequency (ω) of the oscillating magnetic field and especially the rate constant (k2), which corresponds to the wheel speed in the melt spinning technique (MST), on the DMHL are investigated. The shapes and areas of hysteresis loops are affective sensibility by these system parameters. We also investigate the magnetic coercive fields and remanents magnetizations as a function ω. We found that the most of our results are in a good agreement with some theoretical and experimental reported works. We also observe the novel and interesting DMHL behaviors for lower values of T, and higher values of ω, k2 and D.

The quaternary alloy on the Bethe lattice

The quaternary alloy (QA) is simulated on the Bethe lattice (BL) in the form of ABpCqDr and its phase diagrams are calculated by using the exact recursion relations (ERR) for the coordination number z = 3. The QA is designed on the BL by placing A atoms (spin-1/2) on the odd shells and randomly placing B (spin-3/2), C (spin-5/2) or D (spin-1) atoms with probabilities p, q and r, respectively, on the even shells. A compact form of formulation for the QA is obtained in the standard-random approach which can easily be reduced to ternary alloy (TA) and mixed-spin models by the appropriate values of the random variables p, q and r. The phase diagrams are calculated on the temperature and ratio of bilinear interaction parameter planes for given values of probabilities.

Quantum heat engine model of mixed triangular spin system as a working substance

In this work, we consider a Heisenberg XXZ mixed (1∕2,1,1∕2) spin system on a triangular cell. We briefly summarize the theoretical framework. Then, we compute the energy eigenvalues for all eigenstates of the Hamiltonian model and we set a four-stroke Otto cycle to depend on the thermodynamical cycle based on the theoretical framework. In the numerical procedure, based on eigenenergies of the system, we compute the work and the efficiency for different spin interaction couplings for the four-stroke quantum Otto cycle. We show that the Heisenberg XXZ mixed spin model produce positive work and efficiency, when the system is coupled to an oscillating heat bath reservoir. Finally, we investigate magnetic field dependence of the work for several spin coupling and discuss all the results.

Spin supersolid phase in coupled alternating spin chains

We study the ground state phase diagram of a two dimensional mixed-spin system of coupled alternating spin-1 and 1/2 chains with a stripe supersolid phase. Utilizing different analytical and numerical approaches such as mean field approximation, cluster mean field theory and linear spin wave theory, we demonstrate that our system displays a rich ground state phase diagram including novel stripe supersolid, solids with different fillings and super-counterfluid phases, in addition to a stripe solid with half filling, superfluid and Mott insulating phases. In order to find a minimal mixed-spin model for stripe supersolidity, in the second part of the paper we consider two kinds of mixed-spin system of coupled alternating spin-1 and 1/2 chains with (i) anisotropic nearest neighbor interactions, (ii) anisotropic hoppings and study their ground state phase diagrams. We demonstrate that, for the systems with uniform hoppings, the repulsive intra-chains interactions are necessary for stripe supersolidity. In this case the minimal two dimensional mixed-spin model is a system of spin-1 and spin-1/2 XXZ chains, interacting via Ising Hamiltonian. In the case of anisotropic hoppings, a system of coupled Ising chains is the minimal model.

The Possibility of Many Compensation Points in a Mixed-Spin Ising Ferrimagnetic System

The magnetic properties of a ferrimagnetic mixed spin-3/2 and spin-5/2 Ising model with different anisotropies are investigated by using the mean-field approximation (MFA). In particular, the effect of magnetic anisotropies on the compensation phenomenon, acting on A-atoms and B-ones for the mixed-spin model, has been considered in a zero field. The free energy of a mixed-spin Ising ferrimagnetic system from MFA of the Hamiltonian is calculated. By minimizing the free energy, we obtain the equilibrium magnetizations and the compensation points. The phase diagram of the system in the anisotropy dependence of transition temperature has been discussed as well. Our results of this model predict the existence of many (two or three) compensation points in the ordered system on a simple cubic lattice.

Mean-Field Solution of a Mixed Spin-3/2 and Spin-2 Ising Ferrimagnetic System with Different Single-Ion Anisotropies

The mixed spin-3/2 and spin-2 Ising ferrimagnetic system with different single-ion anisotropies in the absence of an external magnetic field is studied within the mean-field theory based on Bogoliubov inequality for the Gibbs free energy. Second-order critical lines are obtained in the temperature-anisotropy plane. Tricritical line separating second-order and first-order lines is found. Finally, the existence and dependence of a compensation points on single-ion anisotropies is also investigated for the system. As a result, this mixed-spin model exhibits one, two or three compensation temperature depending on the values of the anisotropies.

Quantum Fidelity and Thermal Phase Transitions in a Two-Dimensional Spin System

We investigate the ability of quantum fidelity in detecting the classical phase transitions (CPTs) in a two-dimensional Heisenberg—Ising mixed spin model, which has a very rich phase diagram and is exactly soluble. For a two-site subsystem of the model, the reduced fidelity (including the operator fidelity and the fidelity susceptibility) at finite temperatures is calculated, and it is found that an extreme value presents at the critical temperature, thus shows a signal for the CPTs. In some parameter region, the signal becomes blurred. We propose to use the “normalized fidelity susceptibility" to solve this problem.

The Computation of Scalar Curvature in the Four-State Mixed Spin Model and the Investigation of Its Behavior: A Computational Study

The following article has been retracted due to the investigation of complaints received against it. Mr. Mohammadali Ghorbani (corresponding author and also the last author) cheated the authors’ name: Alireza Heidari, Foad Khademi,Jahromi and Roozbeh Amiri. The scientific community takes a very strong view on this matter and we treat all unethical behavior such as plagiarism seriously. This paper published in Vol.3 No.4 334-339, 2012, has been removed from this site.

Magnetic Properties of One-Dimensional Ferromagnetic Mixed-Spin Model within Tyablikov Decoupling Approximation

In this paper, we apply the two-time Green's function method, and provide a simple way to study the magnetic properties of one-dimensional spin-(S,s) Heisenberg ferromagnets. The magnetic susceptibility and correlation functions are obtained by using the Tyablikov decoupling approximation. Our results show that the magnetic susceptibility and correlation length are a monotonically decreasing function of temperature regardless of the mixed spins. It is found that in the case of S=s, our results of one-dimensional mixed-spin model is reduced to be those of the isotropic ferromagnetic Heisenberg chain in the whole temperature region. Our results for the susceptibility are in agreement with those obtained by other theoretical approaches.

Mixed spin-3/2 and spin-5/2 Ising system on the Bethe lattice

In order to study the critical behaviors of the half-integer mixed spin-3/2 and spin-5/2 Blume–Capel Ising ferrimagnetic system, we have used the exact recursion relations on the Bethe lattice. The system was studied for the coordination numbers with q = 3 , 4, 5 and 6, and the obtained phase diagrams are illustrated on the ( k T c / | J | , D A / | J | ) plane for constant values of D B / | J | , the reduced crystal field of the sublattice with spin-5/2, and on the ( k T c / | J | , D B / | J | ) plane for constant values of D A / | J | , the reduced crystal field of the sublattice with spin-3/2, for q = 3 only, since the cases corresponding to q = 4 , 5 and 6 reproduce results similar to the case for q = 3 . In addition we have also presented the phase diagram with equal strengths of the crystal fields for q = 3 , 4, 5 and 6. Besides the second- and first-order phase transitions, the system also exhibits compensation temperatures for appropriate values of the crystal fields. In this mixed spin system while the second-order phase transition lines never cut the reduced crystal field axes as in the single spin type spin-3/2 and spin-5/2 Ising models separately, the first-order phase transition lines never connect to the second-order phase transition lines and they end at the critical points, therefore the system does not give any tricritical points. In addition to this, this mixed-spin model exhibits one or two compensation temperatures depending on the values of the crystal fields, as a result the compensation temperature lines show reentrant behavior.

Renormalization-group magnetization of a ferrimagnetic Ising system

We employ a real-space renormalization-group (RSRG) approach to study a mixed-spin (spin- 1 2 and spin-1) antiferromagnetic Ising model on the square lattice. The model incorporates next-nearest-neighbor interactions which are relevant to describe ferrimagnetism. We present an RSRG calculation of the spontaneous magnetization and compensation temperatures of the mixed-spin model. The influence of crystal-field and next-nearest-neighbor interactions on compensation temperatures is studied; the important physical ingredient that leads to the presence of these temperatures is the next-nearest-neighbor coupling between spins 1 2 .

Tricritical behavior in deterministic aperiodic ising systems

We use a mixed-spin model, with aperiodic ferromagnetic exchange interactions and crystalline fields, to investigate the effects of deterministic geometric fluctuations on first-order transitions and tricritical phenomena. The interactions and the crystal-field parameters are distributed according to some two-letter substitution rules. From a Migdal-Kadanoff real-space renormalization-group calculation, which turns out to be exact on a suitable hierarchical lattice, we show that the effects of aperiodicity are qualitatively similar for tricritical and simple critical behavior. In particular, the fixed point associated with tricritical behavior becomes fully unstable beyond a certain threshold dimension (which depends on the aperiodicity), and is replaced by a two-cycle that controls a weakened and temperature-depressed tricritical singularity.

Quantum phase transitions for the Haldane system in higher dimensions: A mixed-spin cluster expansion approach

We present a mixed-spin cluster expansion method to discuss the quantum phase transitions for the Haldane system in two and three dimensions. By mapping the $s=1$ antiferromagnetic spin model on square and cubic lattices to the equivalent mixed-spin model, we study the competition among the Haldane, the dimer, and the magnetically ordered phases. The mixed-spin cluster expansion proposed here realizes the notion of the valence bond solid in a perturbation theory. This method allows us to directly deal with the Haldane phase, which may not be reached by standard series expansion methods. The zero-temperature phase diagram is thus determined rather precisely for the two- and three-dimensional Haldane systems.

Mixed-spin Ising model on the union jack lattice

We show that the mixed-spin Ising model on the union jack lattice with S= 1/2 and S=1 spin operators placed on different sublattices is equivalent to the eight-vertex model. On a two-dimensional manifold in a parameter space, the model corresponds to the symmetric eight-vertex model and thus is solvable. We locate exactly a coexistence surface between two ordered phases of the mixed-spin model. This surface is bounded by a bicritical line with continuously changing exponents.