Mixed Spin System Research Articles

Effect of progressive substitution of spin-3/2 by spin-7/2 on the magnetocaloric properties of a mixed spin binary alloy system: A Monte Carlo study

Using Monte Carlo simulation the concentration dependency of the cooling exponent (n) of a binary alloy AxB1-x mixed spin system (7/2, 3/2) was studied rigorously. For low magnetic field (h) the entropy change (ΔS), excellently follows the relation ΔS∝hn. The exponent n hardly changes with x within the region 0.5 < x < 0.75. But for further increment of x > 0.75, n sharply drops down. The exponent n is strongly affected by the exchange interaction energy (ε). Due to the decrement of the antiferromagnetic interactions n value rapidly decreases. For the increment of x or the number of A(spin-7/2) atom the magnetization M as well as the magnetic entropy change ΔS increases. The phase transition temperature (i.e. Curie temperature) tC linearly decreases for the increase of x.

Hybrid magnonics in hybrid perovskite antiferromagnets

Hybrid magnonic systems are a newcomer for pursuing coherent information processing owing to their rich quantum engineering functionalities. One prototypical example is hybrid magnonics in antiferromagnets with an easy-plane anisotropy that resembles a quantum-mechanically mixed two-level spin system through the coupling of acoustic and optical magnons. Generally, the coupling between these orthogonal modes is forbidden due to their opposite parity. Here we show that the Dzyaloshinskii–Moriya-Interaction (DMI), a chiral antisymmetric interaction that occurs in magnetic systems with low symmetry, can lift this restriction. We report that layered hybrid perovskite antiferromagnets with an interlayer DMI can lead to a strong intrinsic magnon-magnon coupling strength up to 0.24 GHz, which is four times greater than the dissipation rates of the acoustic/optical modes. Our work shows that the DMI in these hybrid antiferromagnets holds promise for leveraging magnon-magnon coupling by harnessing symmetry breaking in a highly tunable, solution-processable layered magnetic platform.

Critical and hysteresis phenomena in the mixed spin-[formula omitted] anisotropic two-dimensional Heisenberg model: A Monte Carlo study

The critical and hysteresis behaviors of the ferromagnetic mixed-spin system consisting of two sublattices A and B with two types of spins SA=32 and SB=12 described by anisotropic Classical-Heisenberg Model on a square lattice are examined by using Monte Carlo simulations based on metropolis algorithm. By exploiting the thermal variations of the order-parameters and the magnetic susceptibility, the phase diagrams are calculated on the (Dz/J,kBT/J), (Dx/J,kBT/J) and (Δ,kBT/J) planes and the effects of various interaction parameters in the Hamiltonian are explored. It is found that the model yields only second-order phase transitions. We have also estimated the critical exponents ν, β and γ of the model as functions of Dz and Dx by using the finite-size scaling arguments and found that they depend on the details of the model. Finally, the hysteresis behavior of the model is also investigated and it is revealed that the width of hysteresis loop decreases with temperature while it increases for positive Dz values.

Ferrimagnetic mixed Ising spin (7/2, 1/2) system: By Mean Field Theory, exact recursion relations and Monte Carlo method

Based on Mean Field Theory, Exact Recursion Relations, and Monte Carlo Simulations, we have studied phase diagrams and magnetic properties of the mixed system of Ising spin-7/2 and spin-1/2 coupled ferrimagnetically. The system consists of two interpenetrating face-centered cubic sublattices of each spin type. A comparative analysis of the obtained results by these methods is developed. Our calculations have shown a qualitatively good agreement between these three methods' results. However, quantitatively, the produced output quantities values by them show a non-negligible difference. The reasons for that quantitative disagreement have been pointed out in the approximations applied in these different methods. These methods remain nevertheless power tools to study such kinds of systems.

The thermal properties of the mixed spin-1/2, 1, 3/2 Ising model on the Bethe lattice

A triple mixed-spin Ising system defined on the Bethe lattice is numerically investigated by means of exact recursion relations (ERRs) calculations. The lattice is constituted by three types of magnetic atoms A, B, C with spins [Formula: see text], [Formula: see text], [Formula: see text] respectively arranged in the form ABCABC. The effects of bilinear exchange and crystal-field interactions as well as those of thermal fluctuations on the order parameters and phase diagrams are thoroughly studied and specified. First-order transitions and tricritical points are present for the coordination number [Formula: see text] whereas at [Formula: see text] they are absent. Global compensation phenomena are absent for the magnetic system. Instead, it is shown that it can only occur between the sublattice magnetizations B and C of the system. Several novel kinds of reentrance of the phase boundaries while varying the values of model parameters have been reported.

Majorana stellar representation for mixed-spin (s, 1/2) systems* *Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0304202 and 2017YFA0205700), the National Natural Science Foundation of China (Grant No. 11875231), and the Fundamental Research Funds for the Central Universities, China (Grant No. 2018FZA3005).

By describing the evolution of a quantum state with the trajectories of the Majorana stars on a Bloch sphere, Majorana’s stellar representation provides an intuitive geometric perspective to comprehend the quantum system with high-dimensional Hilbert space. However, the representation of a two-spin coupling system on a Bloch sphere has not been solved satisfactorily yet. Here, a practical method is presented to resolve the problem for the mixed-spin (s, 1/2) system and describe the entanglement of the system. The system can be decomposed into two spins: spin-(s + 1/2) and spin-(s – 1/2) at the coupling bases, which can be regarded as independent spins. Besides, any pure state may be written as a superposition of two orthonormal states with one spin-(s + 1/2) state and the other spin-(s – 1/2) state. Thus, the whole initial state can be regarded as a state of a pseudo spin-1/2. In this way, the mixed spin decomposes into three spins. Therefore, the state can be represented by (2s + 1) + (2s – 1) + 1 = 4s + 1 sets of stars on a Bloch sphere. Finally, some examples are given to show symmetric patterns on the Bloch sphere and unveil the properties of the high-spin system by analyzing the trajectories of the Majorana stars on the Bloch sphere.

Quantum discord based on linear entropy and thermal negativity of qutrit–qubit mixed spin chain under the influence of external magnetic field

We propose a reliable analytical method to evaluate the non-classical correlations based on linear entropy for an arbitrary qudit–qubit quantum state. The linear entropy is used to overcome the difficulty of the maximization of the classical correlations encountered when the von Neumann entropy is used in determining quantum discord. The quantum discord based on linear entropy is employed to derive the amount of quantum correlations in a qutrit–qubit mixed spin system in the thermal equilibrium at temperature T. We investigate also the situation when the system is embedded in an external magnetic field. The obtained amount of quantum discord is then compared with the measurement-induced disturbance (MID) and logarithmic negativity. The analysis shows that both QD and MID are more robust than entanglement. Besides, QD and MID can be exploited to determine the critical points of quantum phase transitions in the system.

Triple mixed-spin Ising model

The A, B and C atoms with spin-1/2, spin-3/2 and spin-5/2 are joined together sequentially on the Bethe lattice in the form of ABCABC[Formula: see text] to simulate a molecule as a triple mixed-spin system. The spins are assumed to be interacting with only their nearest-neighbors via bilinear exchange interaction parameter in addition to crystal and external magnetic fields. The order-parameters are obtained in terms of exact recursion relations, then from the study of their thermal variations, the phase diagrams are calculated on the possible planes of our system. It is found that the model gives only second-order phase transitions in addition to the compensation temperatures.

Dynamic critical phenomena in a multilayer Ising system

Using the mixed-spin system, we precisely calculate the dynamic critical phenomena, namely dynamic compensation behaviors, dynamic phase diagrams and dynamic hysteresis loops in a multilayer Ising system that composes of four monoatomic layers. As the method, we use the mean-field theory based on Glauber-type stochastic dynamics. It is found that the Hamiltonian parameters have a strong effect on the dynamic critical phenomena. The system displays the P-, Q-, R-, and S-type compensations and multiple hysteresis loop behaviors. The results are qualitatively consistent with those of some theoretical and experimental studies.

Mixed-spin system with supersolid phases: magnetocaloric effect and thermal properties

Recently, it has been shown that two dimensional frustrated mixed-spin systems with anisotropic exchange interactions display supersolid phases in their ground state phase diagrams even in the absence of long-range interactions. In this paper, using cluster mean field theory, we investigate the effects of thermal fluctuations on the ground state phases of this kind of system and show that various thermal solids and thermal insulators emerge around the ground state solid and Mott insulating phases. We also study the thermodynamic properties and magnetocaloric effect of these systems and demonstrate that at low temperatures, a large cooling rate is seen in the vicinity of the solid-supersolid, solid-superfluid and Mott insulator-superfluid critical points, with the large accumulation of the entropy and the minimums of the isentropes. Our results show the sign change of the magnetocaloric parameter inside the solids and the Mott insulator, which is a characteristic of ordered phases.

Residual entropy and spin fractionalizations in the mixed-spin Kitaev model

We investigate the ground-state and finite-temperature properties of the mixed-spin $(s,S)$ Kitaev model. When one of the spins is a half integer and the other is an integer, we introduce two kinds of local symmetries, which results in a macroscopic degeneracy in each energy level. Applying the exact diagonalization to several clusters with $(s,S)=(1/2,1)$, we confirm the presence of this large degeneracy in the ground states, in contrast to conventional Kitaev models. By means of the thermal pure quantum state technique, we calculate the specific heat, entropy, and spin-spin correlations in the system. We find that in the mixed-spin Kitaev model with $(s,S)=(1/2,1)$, at least, the double-peak structure appears in the specific heat and the plateau in the entropy at intermediate temperatures, indicating the existence of spin fractionalization. Deducing the entropy in the mixed-spin system with $s,S\ensuremath{\le}2$ systematically, we clarify that the smaller spin $s$ is responsible for the thermodynamic properties at higher temperatures.

Monte Carlo simulation of dieletric properties of the antiferroelectric/ferroelectric BiFeO3/YMnO3 bilayer in the external electric field

Monte Carlo simulation has been used to study the dielectric properties of an antiferroelectric/ferroelectric Ising bilayer structure which consists of the top layer with spin-5/2 and the bottom layer with spin-2. The effects of the crystal-fields, the exchange couplings and the external electric field on the polarization, the dielectric susceptibility, the internal energy, the specific heat and the blocking temperature of the mixed-spin bilayer system have been examined detailedly. In particular, the phase diagrams of the blocking temperature under the effects of various physical parameters are obtained for the present system. Through a comparison, there is in agreement between our results obtained and other theoretical studies as well as experimental results.

Study of the magnetic properties of the perovskite CeFeO3: Monte Carlo Simulations

In this study, we investigate the magnetic properties of the perovskite CeFeO3, using Monte Carlo Simulations (MCS). This perovskite is modeled by a mixed spin system (5/2, 3/2). In a first part, we have investigated the effect of different physical parameters on the stability of different phases. From 6x4 = 24 possible phases, we found twelve (12) stable phases in the exchange coupling interaction plane. On the other hand, we have inspected the thermal behavior of the magnetizations and the by using MCS. In fact, we have analyzed and presented the effect of the crystal field, the exchange coupling interactions and the external magnetic field on our system. For very low temperature values, the total magnetization reaches its maximum value. This is in good agreement with the ground state phase diagram. The magnetic susceptibility of the perovskite CeFeO3 reaches its maximum value showing a peak at the specific temperature Tc ˜ 12 K. To complete our study; we presented and analyzed the hysteresis loops for specific values of the physical parameters.

XXZ-Ising model on the triangular kagome lattice with spin 1 on the decorated trimers.

We consider the triangular kagome XXZ-Ising model (TKL XXZ-Ising model) formed by inserting small triangles ("a-trimers") with XXZ spin-1 inside the triangles of the kagome lattice ("b-trimers"). It is a mixed spin system and can be solved exactly by transforming into the kagome lattice with the general transformation method for decorated spin systems. In the absence of an external field, we integrate out the quantum spins of the a-trimers and map the TKL model to the kagome Ising model exactly. We obtain the full phase diagram and their zero-temperature entropies (e.g., s_{max}=5.48895 per unit cell is given for the phase with the maximum entropy). When an external field is applied, 20 phases are found due to the quantum fluctuations of a-trimers. Moreover, the high spins in the a-trimers can lead to a stable quantized growth of the magnetization process in the Heisenberg limit.

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.

Magnetic and thermodynamic properties of a ferromagnetic mixed-spin (1/2, 1, 3/2) three-layer film superlattice

Using the Monte Carlo simulation, we have studied the magnetic and thermodynamic properties of a ferromagnetic three-layer film mixed-spin (1/2, 1, 3/2) system. We have discussed the influence of intralayer and interfacial exchange couplings, film thickness, magnetic atom concentration and temperature on the magnetization of the superlattice system, magnetic susceptibility, internal energy and specific heat of the system. The phase diagrams in various parameters planes are obtained. Loads of interesting magnetic behaviors have been found, such as double-peak and triple-peak phenomena in the susceptibility and specific heat curves as well as obvious finite size effects for small layer thickness. Through a comparison, there is qualitatively a good agreement between our results and those of other theoretical and experimental studies.

Random crystal field effects on the integer and half-integer mixed-spin system

In this work, we have focused on the random crystal field effects on the phase diagrams of the mixed spin-1 and spin-5/2 Ising system obtained by utilizing the exact recursion relations (ERR) on the Bethe lattice (BL). The distribution function P(Di)=pδ[Di−D(1+α)]+(1−p)δ[Di−D(1−α)] is used to randomize the crystal field.The phase diagrams are found to exhibit second- and first-order phase transitions depending on the values of α, D and p. It is also observed that the model displays tricritical point, isolated point, critical end point and three compensation temperatures for suitable values of the system parameters.

A mixed-spin Ising system in a graphene layer with higher order exchange interaction couplings

The magnetic properties of a mixed spin $$\sigma =\pm 1/2$$ and spin $$S=\pm 3/2, \pm 1/2$$ Ising ferromagnetic or ferrimagnetic system on a graphene layer have been investigated within the framework of the Monte Carlo simulation. The four-spin interactions, the single-ion anisotropy and the external magnetic field have important effects on the blocking temperature of the system. The influence of the system parameters on the compensation behavior has been discussed also in the present paper.

Low dimensional mixed-spin Ising model with next-nearest neighbor interaction

In this study, the effects of next-nearest neighbor interaction on a one-dimensional mixed spin 3 - spin 3/2 Ising model was investigated using Cellular Automaton (CA). The Ising model hamiltonian contains the antiferromagnetic nearest neighbor interaction (J1), the ferromagnetic next- nearest neighbor interaction (J2) and the external magnetic field (h = H/J1). Magnetization (M) of the mixed spin system was obtained in the interval 0 ≤ R ≤ 1 of the interaction ratio (R = J2/J1) using field cooling (FC) and zero-field cooling (ZFC) processes. Hysteresis curves were drawn for several R values in the interval −0.1 ≤ h ≤ 0.1 using FC results. The functional behavior for coercive field (HC) was determined depending on R. Thus, the mixed spin system became a hard magnetic material and the lattice geometry also changed from one dimensional linear chain to triangular chain with increasing R value.