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Critical behavior of ferromagnetic pure and random diluted nanoparticles with competing interactions: variational and Monte Carlo approaches | | E. A. Velásquez
; J. Mazo-Zuluaga
; Johans Restrepo
; Òscar Iglesias
; | | Date: |
15 Nov 2010 | | Abstract: | The magnetic properties and critical behavior of both ferromagnetic pure and
metallic nanoparticles having concurrently atomic disorder, dilution and
competing interactions, are studied in the framework of an Ising model. We have
used both the free energy variational principle based on the Bogoliubov
inequality and Monte Carlo simulation. As a case of study for random diluted
nanoparticles we have considered the Fe$_{0.5}$Mn$_{0.1}$Al$_{0.4}$ alloy
characterized for exhibiting, under bulk conditions, low temperature reentrant
spin glass (RSG) behavior and for which experimental and simulation results are
available. Our results allow concluding that the variational model is
successful in reproducing features of the particle size dependence of the Curie
temperature for both pure and random diluted particles. In this last case, low
temperature magnetization reduction was consistent with the same type of RSG
behavior observed in bulk in accordance with the Almeida-Thouless line at low
fields and a linear dependence of the freezing temperature with the reciprocal
of the particle diameter was also obtained. Computation of the correlation
length critical exponent yielded the values $
u=0.926pm 0.004$ via Bogoliubov
and$
u =0.71pm 0.04$ via Monte Carlo. This fact indicates that even though
thermodynamical models can be indeed used in the study of nanostructures and
they can reproduce experimental features, special attention must be paid
regarding critical behavior. From both approaches, differences in the $
u$
exponent with respect to the pure Ising model agree with Harris and Fisher
arguments. | | Source: | arXiv, 1011.3388 | | Services: | Forum | Review | PDF | Favorites | |
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