87 research outputs found
Critical and compensation phenomena in a mixed-spin ternary alloy: a Monte Carlo study
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 on a cubic lattice. We focus on the case with the parameters
corresponding to the Prussian blue analog and confront our
findings with those obtained by some approximative approaches and the
experiments.Comment: 20 pages, 8 figure
Phase transitions in a triangular Blume-Capel antiferromagnet
We study the critical behavior of a frustrated Blume-Capel (BC)
antiferromagnet on a triangular lattice by Monte Carlo simulations. For a
reduced single-ion anisotropy strength we find two phase
transitions. The low-temperature phase is characterized by the
antiferromagnetic long-range ordering (LRO) on two sublattices with the third
one remaining in a non-magnetic state. At higher temperatures there is a
critical region of the Berezinskii-Kosterlitz-Thouless (BKT) type with a
power-law decaying spin-correlation function. For ,
there is only one phase transition from the LRO to the paramagnetic region and
the transition is of first order. The presence of the BKT phase in the current
frustrated BC model is a new feature not observed in its non-frustrated
counterparts. The values of the decay exponent of the BKT phase
corresponding to upper and lower temperatures appear to be consistent with the
theoretical predictions for the six-state clock model.Comment: 19 pages, 12 figure
Critical behavior of a triangular lattice Ising AF/FM bilayer
We study a bilayer Ising spin system consisting of antiferromagnetic (AF) and
ferromagnetic (FM) triangular planes, coupled by ferromagnetic exchange
interaction, by standard Monte Carlo and parallel tempering methods. The AF/FM
bilayer is found to display the critical behavior completely different from
both the single FM and AF constituents as well as the FM/FM and AF/AF bilayers.
Namely, by finite-size scaling (FSS) analysis we identify at the same
temperature a standard Ising transition from the paramagnetic to FM state in
the FM plane that induces a ferrimagnetic state with a finite net magnetic
moment in the AF plane. At lower temperatures there is another phase
transition, that takes place only in the AF plane, to different ferrimagnetic
state with spins on two sublattices pointing parallel and on one sublattice
antiparallel to the spins on the FM plane. FSS indicates that the corresponding
critical exponents are close to the two-dimensional three-state ferromagnetic
Potts model values.Comment: 11 pages, 5 figure
Entropy of spin clusters with frustrated geometry
Geometrically frustrated clusters of Ising spins of different shapes on a
triangular lattice are studied by exact enumeration and Monte Carlo simulation.
The focus is laid on the ground-state energy and residual entropy behaviors as
functions of the cluster shape and size, as well as the spin value. Depending
on the cluster shape, the residual entropy density on approach to the
thermodynamic limit can either vanish or remain finite and the dependence can
be decreasing, increasing or non-monotonic. Nevertheless, the relative
entropies normalized by the respective thermodynamic limit values turn out to
be little sensitive to the spin value. Some interesting finite-temperature
properties of the clusters are also discussed and attention is drawn to their
magnetocaloric properties.Comment: 15 pages, 7 figure
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 a
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 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
reentrant phenomenon produced by CVT. Nevertheless, the multicompensation
behavior predicted by MFT and EFT was confirmed.Comment: 14 pages, 5 figure
Frustrated mixed spin-1/2 and spin-1 Ising ferrimagnets on a triangular lattice
Mixed spin-1/2 and spin-1 Ising ferrimagnets on a triangular lattice with
sublattices A, B and C are studied for two spin value distributions and by Monte Carlo
simulations. The non-bipartite character of the lattice induces geometrical
frustration in both systems, which leads to the critical behavior rather
different from their ferromagnetic counterparts. We confirm second-order phase
transitions belonging to the standard Ising universality class occurring at
higher temperatures, however, in both models these change at tricritical points
(TCP) to first-order transitions at lower temperatures. In the model
, TCP occurs on the boundary between paramagnetic and
ferrimagnetic phases. The boundary between two
ferrimagnetic phases and at
lower temperatures is always first order and it is joined by a line of
second-order phase transitions between the paramagnetic and the ferrimagnetic
phases at a critical endpoint. The tricritical behavior
is also confirmed in the model on the boundary between the
paramagnetic and ferrimagnetic phases.Comment: 23 pages, 12 figure
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.Comment: 18 pages, 7 figure
Low-temperature metastable states in a stacked triangular Ising antiferromagnet
We study low-temperature magnetization processes in a stacked triangular
Ising antiferromagnet by Monte Carlo simulations. In increasing and decreasing
magnetic fields we observe multiple steps and hysteresis corresponding to
formation of different metastable states. Besides the equidistant threefold
splitting of the 1/3 ferrimagnetic plateau, we additionally confirm a fourth
plateau in the field-increasing branch and a sizable remanence when the field
is decreased to zero. The newly observed plateau only appears at sufficiently
low temperature and sufficiently large exchange interaction in the stacking
direction. These observations reasonably reproduce low-temperatures
measurements on the spin-chain compound .Comment: 14 pages, 5 figure
Magnetism of the diluted Ising antiferromagnet in a magnetic field on the Kagome lattice: single-spin cluster approximation
An effective-field theory based on the single-spin cluster has been used to
study of a diluted spin- Ising antiferromagnet on the Kagome lattice with
nearest-neighbor interactions. We observe five plateaus in the magnetization
curve of the diluted antiferromagnet when a magnetic field is applied which is
in agreement with Monte Carlo calculation. The effect of the site-dilution on
the magnetic susceptibility is also investigated and discussed. In particular,
we have found that the frustrated Kagome lattice inverse susceptibility fall to
zero at K.Comment: 6 pages, 4 figures, work to be presented at CSMAG conferenc
Phase transitions in a frustrated Ising antiferromagnet on a square lattice
The phase transitions occurring in the frustrated Ising square
antiferromagnet with first- () and second- ()
nearest-neighbor interactions are studied within the framework of the
effective-field theory with correlations based on the different cluster sizes
and for a wide range of . Despite the simplicity of the model,
it has proved difficult to precisely determine the order of the phase
transitions. In contrast to the previous effective-field study, we have found a
first-order transition line in the region close to not only between
the superantiferromagnetic and paramagnetic () but also between
antiferromagnetic and paramagnetic () phases.Comment: 16 pages, 6 figure
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