Abstract
In this paper, the evolutionary algorithms approach is applied to the parameterization of a mathematical model describing the Mössbauer spectra of nanogranular (or nanoparticle) magnetic systems. These systems exhibit physical properties very different from bulk specimens being of great interest for material science and its use as biosensors, magneto sensors, data storage, and magnetic fluids. The purpose of this work is to compare the performance between the Differential Evolution and the Evolutionary Strategies algorithms to optimize the model parameters which best fit the experimental Mössbauer spectra of nanoscale magnetic particles. Spectra of two samples (??iron foil and NiFe2O4 nanoparticles) were recorded, at room temperature, by a conventional Mössbauer spectrometer using a scintillation detector in transmission geometry with a 57Co/Rh source. Fits to Mössbauer spectra were done using spin hamiltonians to describe both the electronic and nuclear interactions; a model of superparamagnetic relaxation of two levels (spin ½) and stochastic theory; a lognormal particle size distribution function as well as a dependency of the magnetic transition temperature and the anisotropy constant on particle diameter. The evolutionary algorithms have been implemented using Python programming language. For comparison, the two algorithms obey the termination criterion of 6,000 evaluations of the objective function. The results presented show the efficiency of these algorithms in the optimization of the parameters and on the fits of the spectra.
Highlights
Magnetic materials and their devices represent a market of over 150 billion dollars each year (GUIMARÃES, 2005)
All experiments involved in this work were carried out in the Physics Department, Federal University of Minas Gerais
In the method commonly used, the parameter values are manually changed by the researcher, who verifies the impact of this change on the model output
Summary
Magnetic materials and their devices represent a market of over 150 billion dollars each year (GUIMARÃES, 2005) As a result, it is a very intense research field. There are plenty of other applications, existing or under development, such as pigments in paintings and ceramics, medical diagnosis, catalysis, magnetic fluids for targeted delivery of drugs in living organisms, and the use as a non-toxic insecticide (DORMANN; FIORANI, 1992; AGUILAR et al, 2014). These particles are the basis of granular magnetic systems, which may be present in the forms of solid grains (ferrites), ferrofluids, and magnetic thin films. Their study generally involves several experimental techniques as Mössbauer spectroscopy, transmission electron microscopy, X-ray diffraction, magnetization, and magnetic susceptibility measurements
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