Mixed Spin Research Articles

Thermodynamic behaviors and hysteresis loops of an edge-modified Kekulene monolayer: A Monte Carlo study

We studied the magnetic and thermodynamic behaviors of an edge-modified Kekulene monolayer using the Monte Carlo method and established the Ising model with the mixed spins of 2 and 5/2. The function curves of temperature on magnetization, susceptibility, internal energy, and specific heat induced by various physical parameters are discussed respectively. The relationship between blocking temperature and various physical parameters is obtained. We also clarify the role of crystal field, exchange coupling and temperature on the hysteresis loops.

The classification of disordered phases of mixed spin (2,1/2) Ising model and the chaoticity of the corresponding dynamical system

We study an Ising model having the mixed spins {±1/2} and {±2,±1,0} on Cayley tree of second-order. We construct the Gibbs measures corresponding to the model and classify the disordered phases associated to the Gibbs measures. Using the compatibility condition, we obtain the system of functional equations associated with the model. Contrary to the Ising model with two different neighbor interactions, we prove that for the given model, the phase transition phenomenon occurs in both the antiferromagnetic and antiferromagnetic regions. Stability analysis of the dynamic system associated with the model is performed at the obtained fixed point. By calculating the Lyapunov exponent numerically, we show that the corresponding dynamical system exhibits the chaotic behavior in some regions. We identify regions where the disordered phases are extreme by means of a tree-indexed Markov chain. We satisfy the Kesten–Stigum condition for non-extremality of the disordered phase according to the fixed point.

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.

Quantum coherence and mutual information of mixed spin-(1/2, 5/2) Ising-<i>XXZ</i> model on quasi-one-dimensional lattices

The mixed spin-(1/2, 5/2) Ising-<i>XXZ</i> model on quasi-one-dimensional lattices can be used to study the properties of some materials (such as heterotrimetallic Fe-Mn-Cu coordination polymer), and the study on this model is beneficial to the practical applications of such materials in the field of quantum information. The quantum coherence and mutual information are calculated by the transfer matrix method, and the effects of Ising interaction, temperature and magnetic field on them are discussed. The results show that the quantum coherence decreases gradually with the increase of Ising interaction at extremely low temperatures, while there is one minimum value of mutual information in an isotropic system and there appear four minimum values in an anisotropic <inline-formula><tex-math id="M3">\begin{document}$\left( {\varDelta = 4} \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230381_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230381_M3.png"/></alternatives></inline-formula> system. Furthermore, quantum coherence and mutual information jump abruptly at quantum phase transition points where the first derivatives of them exhibit singular behaviors. The quantum coherence and mutual information at finite temperatures are also studied. As the temperature increases, they decrease monotonically in a weak magnetic field, but they first increase and then decrease in a higher magnetic field, which is caused by the competition between thermal fluctuation and magnetic field. Compared with quantum mutual information, quantum coherence exists over a wider range of magnetic field and temperature, which can be easily manipulated experimentally.

A new compound Na5Mn4(PO4)4F4·2H2O with a rarely mixed valence spin chain showing multiple magnetic transitions

A new mixed valence Mn3+/Mn2+ spin-chain compound Na5Mn4(PO4)4F4·2H2O shows multiple magnetic transitions at low temperature.

On the second moment method and RS phase of multi-species spherical spin glasses

Excluding some special cases, computing the critical inverse-temperature βc of a mixed p-spin spin glass model is a difficult task. The only known method to calculate its value for a general model requires the full power of the Parisi formula. On the other hand, an easy application of the second moment method to the partition function yields an explicit lower bound βm≤βc to the critical inverse-temperature. Interestingly, in the important case of the Sherrington-Kirkpatrick model βm=βc. In this work we consider the multi-species spherical mixed p-spin models without external field, and characterize by a simple condition the models for which the second moment method works in the whole replica symmetric phase, namely, models such that βm=βc. In particular, for those models we obtain the value of βc.

Random-anisotropy mixed-spin Ising on a triangular lattice

We have studied the mixed spin-1/2 and 1 Ising ferrimagnetic system with a random anisotropy on a triangular lattice with three interpenetrating sublattices A, B, and C. The spins on the sublattices are represented by σA (states ±1/2), σB (states ±1/2), and SC (states ±1, 0). We have performed Monte Carlo simulations to obtain the phase diagram temperature kBT/|J| versus the strength of the random anisotropy D/|J|. The phase boundary between two ferrimagnetic FR1 and FR2 phases at lower temperatures are always first-order for p < 0.25 and second-order phase transition between the FR1, FR2 and the paramagnetic P phases. On the other hand, for values of p ⪆ 0.5, the phase diagram presents only second-order phase transition lines.

Dynamic-dependent selectivity in a bisphosphine iron spin crossover C-H insertion/π-coordination reaction.

Reaction pathway selectivity is generally controlled by competitive transition states. Organometallic reactions are complicated by the possibility that electronic spin state changes rather than transition states can control the relative rates of pathways, which can be modeled as minimum energy crossing points (MECPs). Here we show that in the reaction between bisphosphine Fe and ethylene involving spin state crossover (singlet and triplet spin states) that neither transition states nor MECPs model pathway selectivity consistent with experiment. Instead, single spin state and mixed spin state quasiclassical trajectories demonstrate nonstatistical intermediates and that C-H insertion versus π-coordination pathway selectivity is determined by the dynamic motion during reactive collisions. This example of dynamic-dependent product outcome provides a new selectivity model for organometallic reactions with spin crossover.

Theoretical investigation of compensation point phenomena in a ferrimagnetic mixed spin-3/2 and spin-1 Ising nanoparticle

ABSTRACT We have explored some magnetic characteristics of a mixed spin-3/2 and spin-1 Ising ferrimagnetic square nanoparticle by utilising the finite cluster approximation. The influences of the core and surface shell couplings (Jc, Js), as well as the crystal fields (Dc, Ds) on the critical and compensation behaviour, were investigated. In the absence of crystal fields, a compensation point only exists if Jc is higher than the threshold core coupling J*c, where the dependence of J*c on Js is linear. By introducing the crystal fields, we found a variety of topologies of the compensation temperature with the possibility of double reentrance. In particular, the presence of the core crystal field Dc, according to the Js strength, may lead to one, two, or three compensation points.

Ferrimagnetic Characteristics and Spin Compensation Temperatures of a Mixed Spin-3 and Spin-5/2 Blume–Capel Model

We study the molecular mean-field theory (MMFT) based on the Gibbs–Bogolyubov free energy function of a ferrimagnetic with mixed spin-3 and spin-5/2 for various magnetic crystal fields in the Blume–Capel model. We have evaluated the free energy depending on the trial Hamiltonian operator. By minimizing the free energy of the present system, we have obtained the characteristic features of the longitudinal magnetizations, compensation temperatures, and re-entrant behaviors in the ranges of low temperatures. In particular, we study the effect of magnetic anisotropies on the critical phenomena for the proposed model. The sublattice magnetization dependence of the free energy function has been discussed as well. Our results predict the existence of multiple spin compensation points in the disordered Blume–Capel system for a square lattice.

Mean Value Ensemble Hubbard-U Correction for Spin-Crossover Molecules.

High-throughput searches for spin-crossover molecules require Hubbard-U corrections to common density functional exchange-correlation (XC) approximations. However, the Ueff values obtained from linear response or based on previous studies overcorrect the spin-crossover energies. We demonstrate that employing a linearly mixed ensemble average spin state as the reference configuration for the linear response calculation of Ueff resolves this issue. Validation on a commonly used set of spin-crossover complexes shows that these ensemble Ueff values consistently are smaller than those calculated directly on a pure spin state, irrespective of whether that be low- or high-spin. Adiabatic crossover energies using this methodology for a generalized gradient approximation XC functional are closer to the expected target energy range than with conventional Ueff values. Based on the observation that the Ueff correction is similar for different complexes that share transition metals with the same oxidation state, we devise a set of recommended averaged Ueff values for high-throughput calculations.

Ferromagnetism in LaMnO3-LaFeO3-LaCoO3 mixed spin perovskite oxide solid solution

The solid solution polycrystalline powder sample of LaMnO3 - LaFeO3 – LaCoO3 was synthesized via mixed-oxide method in 1:1:1 ratio by mass by following two step synthesis process (I) synthesis of LaMnO3, LaFeO3 and LaCoO3 by sol – gel method and (II) synthesis of LaMnO3 - LaFeO3 – LaCoO3 polycrystalline solid solution powder by solid state reaction method. The resulting solid solution crystallizes as a blend of orthorhombic and cubic crystal structure (Space group: Pna21 + Pm 3‾ m). The magnetic characterization in this mixed spin oxide solid solution reveals ferromagnetic nature from 50 K to 300 K. The appearance of stepped hysteresis loop (M − H plot) with two magnetic saturation states at 50 K is the characteristic exclusively exhibited by mixed spin oxide solid solution. Above 50 K only single magnetic saturation state exists with persistent hysteresis loop, thus, confirming the ferromagnetic nature up to 300 K.

Study of the Blume–Emery–Griffiths Model for Mixed Carbon-Like Nanotube: Monte Carlo Study

Monte Carlo study under the Metropolis algorithm is performed to investigate the ground state phase diagrams and hysteresis electric cycles by using the Blume–Emery–Griffiths (BEG) model with the mixed spins (S-1, σ-3/2). Firstly, the ground state phase diagram has been established to show the more stable configurations corresponding to the physical parameter EZ/JC. Moreover, the hysteresis electric cycle behaviors have been investigated by varying temperature, exchange coupling interactions, crystal field and biquadratic parameters of the carbon-like nanotube. It is found that the increase in the crystal field and the biquadratic exchange parameters decrease the surface of the loops leading to the apparition of the polarization plateaus.

Dielectric Properties of Ovalene-Like Nanostructure with RKKY Interactions: Monte Carlo Study

In this study, we investigated the dielectric properties of ovalene-like nanostructure with RKKY (Ruderman–Kittel–Kasuya–Yoshida) interactions, using Monte Carlo simulations. Nanosystem consists of an ovalene-like nanostructure with mixed spins [Formula: see text]-7/2 and S-1, separated by non-electric layers (NEL). We investigated the effect of the non-electric layers, external longitudinal electric field and ferrielectric exchange coupling on polarization and dielectric susceptibility of the nanostructure. We find that the transition temperature is affected by an increase in the number of non-electrical layers. These results can enrich the dielectric properties of ovalene-like nanostructure for future nanotechnology applications.

Static and dynamic magnetic properties in two-dimensional Lieb-like lattice

• Mixed spin Ising model was proposed to describe two-dimensional Lieb-like lattice. • Influence of the periodically oscillating magnetic field on the magnetism of two-dimensional Lieb-like lattice have been investigated. • Multiple compensation temperatures were discovered. The phase diagram and magnetization of a two-dimensional Lieb-like lattice consisting of magnetic atoms with mixed spins 5/2, 3/2, and 2 were investigated based on the effective-field theory with correlations. They exhibited a compensation point below their phase transition temperatures, reentrant behavior, and depressed saturation magnetization within typical parameters of exchange couplings and anisotropies. In addition, the influence of a periodically oscillating magnetic field on the dynamic order parameters of a two-dimensional Lieb-like lattice is discussed. These results can help further understand two-dimensional materials' static and dynamic magnetic properties. Ising model of two-dimensional Lieb lattice is constructured and the Static and dynamic magnetic properties have been investigated for the system.

Dynamic Magnetic Features of a Mixed‐Spin‐2 and Spin‐5/2 Ising Ferrimagnetic System under a Time‐Dependent Oscillating Magnetic Field: Path Probability Method Approach

A study, within the path probability method, of the dynamic magnetic features of the mixed spin (2, 5/2) Ising ferrimagnetic system on a hexagonal lattice under the presence of a sinusoidal external magnetic field is presented. The Hamiltonian of the system contains intersublattice, intrasublattice, and crystal‐field interactions. The intersublattice interaction is taken as antiferromagnetic. The time variations of average dynamic magnetizations and the thermal behavior of the dynamic magnetizations are investigated to obtain the phases in the system and to characterize the nature of the dynamic phase transitions and find the dynamic phase transition temperature points. The dynamic phase diagrams in six different phase planes are presented, in which they contain the paramagnetic (p) phase, three different ferrimagnetic (i 1, i 2, i 3) fundamentals, and the p + i 1, i 1 + i 2, and i 2 + i 3 mixed phases as well as the dynamic tricritical point and the dynamic double critical end point, depending on the interaction parameters. The dynamic compensation behavior is also examined and only N‐type behaviors are observed. Some of the obtained dynamic phase diagrams are in qualitatively good agreement within some works on the dynamics of mixed‐spin Ising system.

Magnetic properties of bond-diluted nanoribbons with hexagonal and rectangular shape

An exploration of the magnetic behavior of bond-diluted mixed spin-3/2 and spin-1/2 Ising model on hexagonal and rectangular nanoribbons is considered by means of the finite cluster approximation. The effects of the bond concentration p and the crystal field D on the phase diagrams yield satisfactory results. In particular, it is found that a horizontal reentrance appears for both nanosystems; while the tricritical phenomenon may occur by the inclusion of the crystal field according to specific Hamiltonian parameters for the rectangular nanoribbon. The dependence on temperature of the total, σ- and S- sublattice magnetizations, mainly at the ground state has also emphasized the significance of the dilution in dominating the magnetic and critical characters.

Compensation temperature and dynamic magnetic properties in the double-layer structure of graphyne-like

The physical properties of the double-layer structure of graphyne-like described by the Ising model were studied by effective-field theory with correlations. The system is composed of mixed spin 5/2 and 2 with ferrimagnetic exchange couplings. The magnetization curve of the system can be divided into three types: P-, Q-, and N-types. Multiple compensation temperatures on the magnetization curve were found within a range of parameters. In addition, the influence of a periodically oscillating magnetic field on the magnetization of the double-layer structure of graphyne-like is discussed. The results indicated that the disorder and order of the system could be controlled and induced by a time-dependent and independent magnetic field.

Monte Carlo study of the phase diagrams and hysteresis behaviors of a ternary mixed spin-(1, 1/2, 3/2) Ising nanowire with ferromagnetic core/ferrimagnetic shell structure

The hysteresis properties and phase diagrams of a ternary nanowire, composed of a ferromagnetic (FM) core of spin-1 encircled by a ferrimagnetic (FiM) shell of mixed spin-(1/2, 3/2). Monte Carlo simulation is used to study the effects of the exchange interactions (Rs, R1, R2 and RIF) and crystal fields (Dc, Ds) on the phase diagrams for various thicknesses of core and shell of the system. Our outcomes indicate that the compensation temperature exists for a particular range when Dc and Ds are present. In addition, a first and a second order phase transitions appear for different values of Dc, while a second phase transition appears for various values of Ds. Moreover, the hysteresis loops, coercivities and remanences of the system and three sublattices are discussed in detail. Multiple hysteresis loops such as double, triple and quintuple loops were found in the system for a various physical parameters. By comparing our findings to those of previous theoretical and experimental studies, a qualitative agreement can be found.

Effect of defects on a nano-borophene structure consisting of mixed spins S = 2 and σ = 5/2: Monte Carlo simulations

Effect of defects on a nano-borophene structure consisting of mixed spins S = 2 and σ = 5/2: Monte Carlo simulations