Ising Nanoparticles Research Articles

Unique phenomena induced by an exchange interaction between two graphene-like Ising nanoparticles in an applied transverse field

The phase diagrams and the magnetizations of graphene-like nanoparticles which are constructed from two paramagnetic honeycomb units and an inter-unit exchange interaction r are investigated by using the effective-field theory with correlations. They have exhibited some characteristic phenomena, such as the reentrant phenomena, when the value of r is larger than r = 1.0 and a transverse field is applied.

Magnetism in a graphene-like Ising nanoparticle under an applied transverse field

The phase diagram and magnetization curves of two antiferromagnetic and ferromagnetic hexagonal Ising nano-particles with a next-next-nearest-neighbor exchange interaction which comes from the super-exchange interaction via a central nonmagnetic atom are investigated by using the effective-field theory with correlations. They have exhibited some characteristic features, such as the reentrant phenomena, when a finite transverse field is applied.

Phase Diagrams in Graphene-like Ising Nanoparticles

The phase diagrams of four graphene-like nanoparticles described by the Ising model are investigated by the use of the effective-field theory with correlations. The particle is represented by a two-dimensional array of spin-1/2 atoms with two types of exchange interactions, J and JS. The effects of surface exchange interaction JS on the phase diagrams are examined. We have found some characteristic behaviours.

Some hysteresis loop features of 2D magnetic spin-1 Ising nanoparticle: shape lattice and single-ion anisotropy effects

The effects of longitudinal and transverse crystal-fields on the magnetic hysteresis behaviors of 2D spin-1 Ising nanoparticles are investigated, by using the effective-field theory based on the probability distribution technique with correlations. Nanoparticles with hexagonal or square lattice are studied. A number of characteristic phenomena such as triple and quadruple hysteresis loop behaviors have been observed for certain physical parameters, originating from the competitions among the core/shell exchange interaction, anisotropies, temperature and the longitudinal magnetic field. Finally, the obtained results are compared with some experimental and theoretical results.

Reentrant phenomenon in a transverse spin-1 Ising nanoparticle with diluted magnetic sites

In the present work, we have examined the influence of surface shell exchange coupling on the magnetic properties of a diluted ferromagnetic spin- 1 Ising nanocubic particle, by employing the effective-field theory with correlations based on the probability distribution technique. Some interesting results have been found such as, a tricritical point, a triple point, an isolated critical point, reentrant and even double reentrant phenomena, S-, R- and Q-type behaviors, as well as, both first- and second-order phase transitions as it is confirmed by the free energy. In addition, when the interactions are low between the surface shell sites, quadruple hysteresis loops can be seen in the system.

Monte Carlo study of magnetic and thermodynamic properties of a ferrimagnetic Ising nanoparticle with hexagonal core-shell structure

The Monte Carlo method has been used to study the magnetic and thermodynamic properties of a hexagonal ferrimagnetic Ising nanoparticle with spin-3/2 inner core surrounded by spin-1 surface shell layers. The effects of exchange couplings and crystal-fields on the compensation behaviors and critical phenomena of the system have been investigated in detail. Many types of the magnetization curves have been found, depending on the competitions among the exchange couplings, the crystal-fields and the temperature. The phase diagrams for different exchange couplings and crystal-fields have been also obtained. In Particular, we have discovered the double and triple hysteresis loops for certain physical parameters in the present system. An excellent agreement has been achieved from the comparison between our results and the previous studies.

Some characteristic behaviours of a spin-1/2 Ising nanoparticle

By using the effective-field theory with correlations based on the probability distribution technique; the magnetization, susceptibility, internal energy, specific heat and the free energy expressions for a ferromagnetic spin-1/2 Ising nanoparticle have been developed and calculated numerically for different surface shell exchange coupling parameter. A number of interesting phenomena have been observed, depending on the surface shell exchange coupling term.

Investigation of a core/shell Ising nanoparticle: Thermal and magnetic properties

The phase diagrams and magnetic hysteresis behavior of a spin-12 Ising core/shell nanoparticle are investigated by the use of the effective field theory with a probability distribution technique that accounts for the self-spin correlation functions. Nearest-neighbor pair interactions are incorporated between the Ising spins in the three parts of the nanoparticle that are core, core/shell and surface shell. The effects of the external magnetic field and core/shell exchange interaction on the thermal magnetization and susceptibility of the system are examined.

Magnetic properties of mixed spin (1, 3/2) Ising nanoparticles with core–shell structure

The magnetic properties of mixed spin-1 and spin-3/2 Ising nanoparticles with core/shell structure are studied by using the effective-field theory with correlations. We investigate the thermal variations of the core, shell and total magnetizations and the Q-, R-, P-, S-, N- and L-types of compensation behavior in Néel classification nomenclature exists in the system. The effects of the crystal-field, core and shell interactions and interface coupling, on the phase diagrams are investigated in detail and the obtained phase diagrams are presented in three different planes. The system exhibits both second- and first-order phase transitions besides tricritical point, double critical end point, triple point and critical end point depending on the appropriate values of the interaction parameters. The system strongly affected by the surface situations and some characteristic phenomena are found depending on the ratio of the physical parameters in the surface shell and the core.

Transverse Ising nano-systems: Unconventinal surface effects

The phase diagrams and temperature dependences of magnetizations in core–shell transverse Ising nanosystems, namely nanowire, nanotube and nanoparticles, are studied by the use of the effective-field theory with correlations (EFT). Some novel and universal features, such as the possibility of re-entrant phenomena being free from disorder induced frustration, are obtained for the magnetic properties in such systems.

Magnetic properties of a single transverse Ising ferrimagnetic nanoparticle

Using the effective field theory with a probability distribution technique that accounts for the self-spin correlation function, the thermal and the magnetic properties of a single Ising nanoparticle consisting of a ferromagnetic core, a ferromagnetic surface shell and a ferrimagnetic interface coupling are examined. The effect of the transverse field in the surface shell, the exchange interactions between core/shell and in surface shell on the free energy, thermal magnetization, specific heat and susceptibility are studied. A number of interesting phenomena have been found such as the existence of the compensation phenomenon and the magnetization profiles exhibit P-type, N-type and Q-type behaviors.

Thermal and magnetic properties of ternary mixed Ising nanoparticles with core–shell structure: Effective-field theory approach

We propose a ternary Ising spins (1/2, 1, 3/2) model to investigate the thermal and magnetic properties of magnetic nanoparticles with core–shell structure within the framework of the effective-field theory with correlations. The center site of the core is occupied by σ=±1/2 spin, while those surrounding the center site are occupied by S=±1, 0 spins and the shell sites are occupied by m=±1/2,±3/2 spins. Thermal behaviors of the core and shell magnetizations, susceptibilities and internal energies as well as total magnetization are examined. In order to confirm the stability of the solutions we also investigate the free energy of the system. According to the values of Hamiltonian parameters, the system undergoes first- and second-order phase transitions. Phase diagrams are calculated and discussed in detail. We find that the system exhibits a tricritical point, reentrant and five different type (Q, P, R, S and W) of compensation behaviors that strongly depend on interaction parameters. The results are in good agreement with some experimental and theoretical results.

Magnetic properties of mixed Ising nanoparticles with core-shell structure

Magnetic properties of Ising nanoparticles with spin-1/2 core and spin-3/2 shell structure are systematically studied by the use of the effective-field theory with correlations. Particular emphasis is given to the effects of the crystal-field, core and shell interactions and interface coupling on magnetizations, compensations points, magnetic susceptibilities and hysteresis behaviors. In order to confirm the stability of the solutions we also investigate the free energy of the system. According to values of Hamiltonian parameters, the system only undergoes a second-order phase transition. A number of characteristic behaviors are found, such as the existence of triple hysteresis loops for appropriate values of the system parameters affected by the crystal field, temperature, and interface coupling. Moreover, Q-, R-, N-, M-, P- and S-types of compensation behaviors in the Neel classification nomenclature exist in the system that are also strongly dependent on interaction parameters; hence, one or two compensation points have been found. The results are compared with those of recently published works and a qualitatively good agreement is found.

Shape dependences of magnetic properties in 2D Ising nano-particles

The shape dependences of magnetic properties (phase diagram and magnetization) in two (circle and square) 2D Ising nano-particles are investigated by the use of both the core-shell model and the effective field theory with correlations, in order to clarify the effects of the shape difference to them. Particular emphasis is given to the effect to the magnetizations when the core-shell exchange coupling takes a different (positive or negative) sing. Some common phenomena are also found in the magnetic properties between the two nanosystems.

The possibility of a compensation point induced by a transverse field in transverse Ising nanoparticles with a negative core–shell coupling

The phase diagram and magnetizations of two 2D nanoparticles with a negative core–shell interaction, described by the transverse Ising model, are investigated by the use of the effective field theory with correlations. The behaviors of a compensation point in these nanosystems are examined by changing an applied transverse field. It is proved that a compensation point can be induced in the two nanosystems by applying a transverse field.

Phase Diagram of Ising Nano-Particles with Cubic Structures

The method of variational cumulant expansion (VCE) on the Ising model is applied to investigate phase transitions in magnetic alloy nano-particles, in which a random site distribution of component atoms is assumed. By introducing the effect exchange constant, it is shown numerically that nano-particles can be treated the same way as bulk materials. The Curie temperature and the Neel temperature of binary magnetic nano-particles with cubic lattices are calculated. It is found that both the Curie temperature and the Neel temperature decrease with decreasing size of the nano-particle. Phase diagrams of binary alloy nano-particles are investigated for variable doping concentration and the results are discussed. As the nano-particle size grows larger, the critical point approaches that of a bulk. On the other hand, the tri-critical point is independent of the nano-particle size and is always the same as that of the bulk.