The study of spin Glass state in Diluted Magnetic materials and semiconductors using monte carlo method and Theoretical Analysis
No Thumbnail Available
Date
2013-03
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Spin glass system is a complex disordered system with a number of local minima
separated by entropic barriers. Therefore, Parallel tempering Monte Carlo simulation
was used in order to get fast thermalisation (to minimize the relaxation time).
Distance dependent interaction coupling in 2D is studied in order to show how a
spin glass phase transition occurs when couplings between far away spins are permitted
by considering Edwards-Anderson Ising spin glass model. The interaction
coupling is a quenched random variable whose probability of being non-zero decays
with distance between two spin sites rij = |i−j|mod(L/2). The interaction coupling
is random and its probability distribution is decaying with the distance between the
spins (p(Jij) / r− ). The model is studied by changing among three different
regimes ( > 2D, 4/3D < < 2D, < 4/3D) . A phase transition temperature for
= 2, 3, 4 is obtained.
In the present work, the possibility of existence of spin glass phase using classical
Heisenberg model with Edwards-Anderson type of interactions has been explored
employing Monte Carlo simulation of Binder parameter (g (L, T)). Previous experimental
studies show that there is finite temperature phase transition but this study
indicates that there is no finite temperature phase transition in 3D Heisenberg vector
spin glass model.
In the dissertation we also explore magnetic properties especially spin glass state,
antiferromagnetic state and paramagnetic state of diluted magnetic semiconductors
(A1−xMnxA0(A = Zn,Cd and A0 = S, Te, Se)) at critical region using classical
Heisenberg spin model with high temperature series expansion extrapolated with
vii
pad´e approximants. The critical exponents associated with magnetic susceptibility
(
' 1.38 ± 0.1) and correlation function ( ' 0.8 ± o.1) were also obtained
Description
Keywords
The study of spin Glass state