Effects Of Random Crystal Field Research Articles

Random crystal field effects on antiferromagnetic spin-1 Blume–Capel model

The outcome of the random crystal field effects on the antiferromagnetic spin-1 Blume–Capel model and external magnetic field are examined on the Bethe Lattice in terms of exact recursion relations. It is assumed that the crystal field is either turned on or off randomly with probability [Formula: see text] and [Formula: see text], respectively. The phase diagrams are constructed from the thermal analysis of the order parameters with the coordination number [Formula: see text] which corresponds to honeycomb lattice. It is explored that the system goes both second- and first-order phase transitions, along with the reentrant behavior and a few critical points. The reentrant behavior is stronger for lower values of [Formula: see text] and disappears as [Formula: see text] gets closer to 1.0. The first-order lines are observed to be either linked to the tricritical points or decomposed. The critical end points and double critical points are also observed.

Antiferromagnetic Spin-3/2 Ising Model Under the Influence of Random Crystal Field

The critical behaviors of the antiferromagnetic spin-3/2 Ising model are studied by using the exact recursion relations (ERR) in the presence of a random crystal field on the Bethe lattice (BL). The sublattice order parameters, magnetizations, and quadrupolar moments are obtained in terms of ERRs under the effect of random crystal field which was either turned on or off with probability p and 1 − p, respectively, in a bimodal form. The nature of phase transitions, thus, the phase diagrams of the model are calculated on the (H, T) planes for the randomly changing crystal field values with probability p for the coordination numbers q = 3 and 4. It is found that the model exhibits both second- and first-order phase transitions in addition to some critical points, i.e., tricritical point (TCP), critical end point, double critical point, and isolated end point. We have also observed the reentrant behavior for some values of our system parameters.

Random crystal-field effects in a mixed spin-1/2 and spin-2 ferrimagnetic Ising system

The magnetic properties of a mixed spin ferrimagnetic system σ = 1/2 and S = 2 at the sites of a square lattice with a random crystal field are studied by the mean field approximation. The ground state of the system is determined and the total magnetization is plotted according to the model parameters. Different behaviors for the thermal dependence of the magnetization are highlighted. In particular, one sees the appearance of one or two compensating points and many types of phase diagrams with first and second order phase transition lines as well as isolated critical and tricritical points.

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.

Random Crystal Field Effect on the Kinetic Spin-1 and Spin-3/2 Under a Time-Dependent Oscillating Field Phase Transitions

The effect of random crystal field on the stationary states of the kinetic spin-1 and spin-3/2 Blume-Capel model is investigated within the framework of the mean field approach. The Glauber-type stochastic dynamics is used to describe the time evolution of the system which is subjected to a time-dependent oscillating external magnetic field. The model exhibits first- and second-order transitions as well as dynamical tricritical, triple and an isolated critical end points. We found that the system displays reentrant phenomenon for both α = 0 and α > 0. Moreover, the system exhibits in the phase space a fixed points and limit cycles with circle, elliptic and parallelogram shapes.

Random crystal field effect on hysteresis loops and compensation behavior of mixed spin-(1,3/2) Ising system

Magnetic hysteresis and compensation behavior of a mixed spin-(1, 3/2) Ising model on a square lattice are investigated in the framework of effective field theory based on a probability distribution technique. The effect of random crystal field, ferromagnetic and ferrimagnetic exchange interaction on hysteresis loops and compensation phenomenon are discussed. A number of characteristic phenomena have been reported such as the observation of triple hysteresis loops at low temperatures and for negative values of random crystal field. Critical and double compensation temperatures have been also found. The obtained results are also compared to some previous works.

A Monte Carlo study of the Blume–Capel thin film in the presence of a random crystal field

A Monte Carlo simulation with heat bath algorithm is used to study the effect of random crystal field and surface exchange interactions on the critical behavior and the magnetic properties of a spin-1 Ising ferromagnetic thin film having the simple cubic symmetry. The phase diagram exhibits a rich variety of behaviors such as the double reentrant phenomena and the existence of tricritical points. Thermal magnetization behavior and phase diagrams have been discussed in detail.

Random crystal-field effects in a mixed spin-1 and spin-3/2 ferrimagnetic Ising system

We study the mixed spin-1 and spin-3/2 ferrimagnetic Ising system under the effect of different random crystal-fields within the mean-field theory based on the Bogoliubov inequality for the Gibbs free energy. The phase diagrams are obtained in the plane of critical temperature versus random crystal-field, showing a tricritical behavior with second-order transition lines separating the first-order transition lines by tricritical points.

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

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.

Spin-1 Blume–Capel model with random crystal field effects

The random-crystal field spin-1 Blume–Capel model is investigated by the lowest approximation of the cluster-variation method which is identical to the mean-field approximation. The crystal field is either turned on randomly with probability p or turned off with q=1−p in a bimodal distribution. Then the phase diagrams are constructed on the crystal field (Δ)–temperature (kT/J) planes for given values of p and on the (kT/J,p) planes for given Δ by studying the thermal variations of the order parameters. In the latter, we only present the second-order phase transition lines, because of the existence of irregular wiggly phase transitions which are not good enough to construct lines. In addition to these phase transitions, the model also yields tricritical points for all values of p and the reentrant behavior at lower p values.

Effect of random crystal field on semi infinite system

The effect of random crystal-field on the magnetic properties of the semi-infinite system is investigated by the use of the mean field approximation. In this system, the sites of the surface and bulk are occupied by spin- 1/2 and spin-1, respectively. The appearance of the partly ferromagnetic phase, in bulk, gives rise to different types of topology of phase diagrams. The system exhibits tricritical and multicritical points.

Random crystal field effects for spin-3/2 Blume–Capel model

The effects of crystal field ( Δ ) which is randomly turned on with probability p or turned off with probability 1− p on the sites of the Bethe lattice are investigated to study the critical behavior of the spin-3/2 Blume–Capel model. The order-parameters are obtained in terms of the recursion relations and then the possible phase diagrams are calculated at finite temperatures for given system parameters p, Δ and coordination numbers z=3, 4, 5 and 6. It was found that the phase diagrams change drastically for given probability and randomness. The first-order phase transitions are only found for higher p values and the lines of which get shorter and eventually disappear as p decreases. The critical lines do not present any qualitative differences with z, but they are seen at higher temperatures for higher z.

Effect of random crystal field on a doubly decorated ferrimagnetic Ising model

Within the framework of the mean-field approximation, we discuss the effects of random crystal field on magnetic properties of the doubly decorated ferrimagnetic Ising model, in which the two magnetic atoms A and B have spins б = ±1/2 and S = ±1, 0, respectively. Also, the effect of the exchange interaction, between nearest neighbor decorating points, on the compensation temperatures is discussed. Furthermore, the appearance of the partly ferrimagnetic phase (m б = −1/2, m s = 1/2) exhibits different types of phase diagrams.

Effects of random-crystal-field on the kinetic Blume Capel model

The effects of random crystal field on the stationary states of the kinetic spin-1 Blume Capel model are studied using the Glauber-type stochastic dynamics under the time-dependent oscillating field assumption. Our investigation, based on the equilibrium ground state phase diagram, revealed many interesting phenomena. The known phases, in the equilibrium case, are obtained for high field and are represented by limit cycles. The phase diagram of the pure pure kinetic Ising spin- 1 2 and spin-1 Blume Capel models are deduced as particular cases. First-order, second-order transition lines, dynamical critical and dynamical double critical end points are also obtained.

Decorated ferrimagnetic Ising model with a random crystal field

A mean-field approximation is used to study the effects of random crystal field on the critical behaviour of decorated ferrimagnetic Ising model, in which the two magnetic atoms A and B have spins σ A = 1 2 and S B = 1 , respectively. The results indicate that there may exist some interesting phenomena in the system, such as the appearance of a new ferrimagnetic phase, namely partly ferrimagnetic phase, and the possibility of one or two compensation temperatures. Re-entrant phenomena can be seen for appropriate ranges of crystal field. Phase diagrams and magnetization curves are investigated in details.

Magnetic order and excitations in amorphous ferromagnets

Neutron polarisation techniques have been used to show that the magnetic structure of Fe-based ferromagnets is not a collinear structure. The degree of canting varies with the sample and there is little correlation in the canting from site to site. In Fe-Ni materials the degree of canting is increased with increasing Ni concentration. The canting arises either from random crystal-field effects or from competing exchange interactions. The measurements also showed inelastic scattering which is different from spin-wave scattering and may arise from the excitations responsible for the temperature dependence of the magnetisation.