Electric Field And Pressure Enhanced Magnetic Properties Of Multiferroic Materials And Bifeo3 And Enhancement Of Critical Temperature Of Superconductor(smasfeof) Under Pressure

In this dissertation we have studied electric field enhanced magnetic properties ofrnmultiferroic materials . The system contains a ferromagnetic and a ferroelectric subrnlattices. To describe the property of system, we considered linear couplingHamiltonianrnbetween ferromagnetism and ferroelectricity without microscopic derivation.rnThe thermodynamic properties of the system are calculated, such as magnon excitationrnspectrum , temperature dependences of magnetization, internal energy,rnspecific heat capacity, and magnetic susceptibility subjected to electric and magneticrnfields. In addition to this electronic and structural properties of multiferroicrnmaterial(BiFeO3) are studied using density functional theory. We also investigaterncritical temperature of iron based superconductors (SmAsFeOF) under the influencernof an external hydrostatic pressure based on density functional theory calculationsrnusing Vasp and quantum Espresso Code coupled with Migdal Eliashbergrnmodel. Our results show that the critical temperature increases up to 45.91K underrnthe pressure upto 30GPa and, subsequently, drops down until 60GPa. Throughoutrnthis pressure range, the system is preserving the initial symmetry without any structuralrntransformation. Our results indicate that the enhancement of critical temperaturernis due to increase electron boson (phonon/spin fluctuation) coupling and furtherrnincrease of pressure may lead to instability of system. Our theoretical resultsrnare in agreement with the experiments.

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