1,122 research outputs found
A Monte Carlo study of critical properties of strongly diluted magnetic semiconductor (Ga,Mn)As
Within a Monte Carlo technique we examine critical properties of diluted bulk
magnetic semiconductor (Ga,Mn)As modeled by a strongly diluted ferromagnetic
Heisenberg spin- system on a face centered cubic lattice. We
assumed that 5\% of Ga atoms is substituted by Mn atoms and the interaction
between them is of the RKKY-type. The considered system is randomly quenched
and a double average was performed: firstly, over the Boltzmann probability
distribution and secondly - over 2048 configurations related to the quenched
disorder. We estimated the critical temperature: K, which is in
agreement with the experiment. The calculated high value of critical exponent
seems to point to a possibility of non-universal critical behavior.Comment: 4 pages, 6 figure
Strongly correlated fermions on a kagome lattice
We study a model of strongly correlated spinless fermions on a kagome lattice
at 1/3 filling, with interactions described by an extended Hubbard Hamiltonian.
An effective Hamiltonian in the desired strong correlation regime is derived,
from which the spectral functions are calculated by means of exact
diagonalization techniques. We present our numerical results with a view to
discussion of possible signatures of confinement/deconfinement of fractional
charges.Comment: 10 pages, 10 figure
Frustration Effects in Antiferromagnetic FCC Heisenberg Films
We study the effects of frustration in an antiferromagnetic film of FCC
lattice with Heisenberg spin model including an Ising-like anisotropy. Monte
Carlo (MC) simulations have been used to study thermodynamic properties of the
film. We show that the presence of the surface reduces the ground state (GS)
degeneracy found in the bulk. The GS is shown to depend on the surface in-plane
interaction with a critical value at which ordering of type I coexists
with ordering of type II. Near this value a reentrant phase is found. Various
physical quantities such as layer magnetizations and layer susceptibilities are
shown and discussed. The nature of the phase transition is also studied by
histogram technique. We have also used the Green's function (GF) method for the
quantum counterpart model. The results at low- show interesting effects of
quantum fluctuations. Results obtained by the GF method at high are
compared to those of MC simulations. A good agreement is observed.Comment: 11 pages, 19 figures, submitted to J. Phys.: Condensed Matte
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