Electric Field and Pressure Enhanced Magnetic Properties of Multiferroic Materials and Bifeo3, and Enhancement of Critical Temperature of Superconductor(Smasfeof) Under Pressure
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Date
2018-03-13
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Addis Ababa University
Abstract
In this dissertation we have studied electric field enhanced magnetic properties of
multiferroic materials . The system contains a ferromagnetic and a ferroelectric sub
lattices. To describe the property of system, we considered linear couplingHamiltonian
between ferromagnetism and ferroelectricity without microscopic derivation.
The thermodynamic properties of the system are calculated, such as magnon excitation
spectrum , temperature dependences of magnetization, internal energy,
specific heat capacity, and magnetic susceptibility subjected to electric and magnetic
fields. In addition to this electronic and structural properties of multiferroic
material(BiFeO3) are studied using density functional theory. We also investigate
critical temperature of iron based superconductors (SmAsFeOF) under the influence
of an external hydrostatic pressure based on density functional theory calculations
using Vasp and quantum Espresso Code coupled with Migdal Eliashberg
model. Our results show that the critical temperature increases up to 45.91K under
the pressure upto 30GPa and, subsequently, drops down until 60GPa. Throughout
this pressure range, the system is preserving the initial symmetry without any structural
transformation. Our results indicate that the enhancement of critical temperature
is due to increase electron boson (phonon/spin fluctuation) coupling and further
increase of pressure may lead to instability of system. Our theoretical results
are in agreement with the experiments.
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Keywords
Electric Field, Pressure Enhanced, Magnetic Properties, Multiferroic Materials