M. Žukovič

Phase diagram of a mixed spin-1 and spin-3/2 Ising ferrimagnet

Critical and compensation properties of a mixed spin-1 and spin-3/2 Ising ferrimagnet on a square lattice are investigated by standard and histogram Monte Carlo simulations. The critical temperature is studied as a function of single-ion anisotropy strength. The second order of the phase transition is established by finite-size scaling for the entire boundary. Some previously obtained results, such as a tricritical point, predicted by the mean field theory (MFT) and the effective field theory (EFT), or a first-order transition line separating two different ordered phases, obtained by the cluster variational theory (CVT), are deemed artifacts of the respective approximations. So is a re-entrant phenomenon produced by CVT. Nevertheless, the multicompensation behavior predicted by MFT and EFT was confirmed.

Critical and compensation phenomena in a mixed-spin ternary alloy: A Monte Carlo study

Abstract By means of standard and histogram Monte Carlo simulations, we investigate the critical and compensation behaviour of a ternary mixed spin alloy of the type ABpC1−p on a cubic lattice. We focus on the case with the parameters corresponding to the Prussian blue analog ( Ni p II Mn 1 − p II ) 1.5 [ Cr III ( CN ) 6 ] · n H 2 O and confront our findings with those obtained by some approximative approaches and the experiments.

Thermodynamic and magnetocaloric properties of geometrically frustrated Ising nanoclusters

Thermodynamic and magnetocaloric properties of geometrically frustrated Ising spin clusters of selected shapes and sizes are studied by exact enumeration. In the ground state the magnetization and the entropy show step-wise variations with an applied magnetic field. The number of steps, their widths and heights depend on the cluster shape and size. While the character of the magnetization plateau heights is always increasing, the entropy is not necessarily decreasing function of the field, as one would expect. For selected clusters showing some interesting ground-state properties, the calculations are extended to finite temperatures by exact enumeration of densities of states in the energy-magnetization space. In zero field the focus is laid on a peculiar behavior of some thermodynamic quantities, such as the entropy, the specific heat and the magnetic susceptibility. In finite fields various thermodynamic functions are studied in the temperature-field parameter plane and particular attention is paid to the cases showing an enhanced magnetocaloric effect. The exact results on the finite clusters are compared with the thermodynamic limit behavior obtained from Monte Carlo simulations.

Phase diagram of a diluted triangular lattice Ising antiferromagnet in a field

Magnetization processes and phase transitions in a geometrically frustrated triangular lattice Ising antiferromagnet in the presence of an external magnetic field and a random site dilution are studied by the use of an effective-field theory with correlations. We find that the interplay between the applied field and the frustration-relieving dilution results in peculiar phase diagrams in the temperature-field-dilution parameter space.

Effects of selective dilution on phase diagram and ground-state magnetizations of an Ising antiferromagnet on triangular and honeycomb lattices

Abstract We employ an effective-field theory with correlations in order to study the phase diagram and ground-state magnetizations of a selectively diluted Ising antiferromagnet on triangular and honeycomb lattices. Dilution of different sublattices with generally unequal probabilities results in a rather intricate phase diagram in the sublattice dilution parameters space. In the case of the frustrated triangular lattice antiferromagnet the selective dilution affects the degree of frustration which can lead to some peculiar phenomena, such as reentrant behavior of long-range order or unsaturated sublattice magnetizations at zero temperature. The selectively diluted Ising antiferromagnet on the honeycomb lattice is obtained as a special case when one sublattice of the triangular lattice is completely removed by dilution.

Thermal and percolative properties of a diluted Ising metamagnet in a field

We calculated thermodynamic quantities such as the staggered and direct susceptibilities, internal energy and specific heat of a diluted Ising layered metamagnet in an external field, by the use of an effective field theory (EFT) with correlations, developed for this model in our previous paper. We also extensively investigated how an inter- and intra-layer exchange interaction ratio can influence critical, tricritical and percolative properties of the system.

Mixed spin-1/2 and spin-1 Ising ferromagnets on a triangular lattice

By Monte Carlo simulations we study critical properties of the mixed spin-1/2 and spin-1 Ising model on a triangular lattice, considering two different ways of the spin-value distributions on the three sublattices: (1/2,1/2,1) and (1/2,1,1). In the former case, we find standard Ising universality class phase transitions between paramagnetic and magnetic phases but no phase transitions between two distinct magnetic phases (±1/2,±1/2,±1) and (±1/2,±1/2,0) at any finite temperature, except for some interesting non-critical anomalies displayed by response functions. On the other hand, the latter case turns out to be a rare (or perhaps the only) example of a two-dimensional mixed spin-1/2 and spin-1 Ising model on a standard lattice that displays tricritical behavior.

Monte Carlo studies of critical and dynamic phenomena in diluted Ising metamagnet in a field

Abstract Monte Carlo simulations have been used to study critical, tricritical as well as some history-dependent properties of a diluted Ising metamagnet in an external field. Phase boundaries, including location of tricritical points, have been established in a broad concentration range. A first-order transition is estimated to survive down to at least p =0.5, i.e., even in an extreme dilution region. In the region of strong dilution additional shorter simulations on lattices of large linear size have been run in order to study irreversibilities associated with the domain state formation.

Monte Carlo investigation of the tricritical point stability in a three-dimensional Ising metamagnet

We use Monte Carlo simulations to study multicritical properties of an Ising metamagnet in an external field. According to the mean field theory predictions, a three-dimensional layered metamagnet is expected to display a tricritical point decomposition to a critical and a bicritical end point, when a ratio between intralayer ferromagnetic and interlayer antiferromagnetic couplings becomes sufficiently small. Our simulations show no evidence of such a decomposition and produce a tricritical behavior even for a coupling ratio as small as

Critical and tricritical behavior of a selectively diluted triangular Ising antiferromagnet in a field

R=0.01.