The First-principle Calculations And Magnetic Properties In Double Perovskite R₂niMnO₆

Multiferroic materials with ferroelectric and ferromagnetic properties within single phase have drawn great attention in publics due to their potential applications for inductive devices,spintronic devices as well as microwave devices in last decades.The future research direction focuses on novel multiferroic materials exploration,such as perovskite structure with abundant structures and excellent properties.In details,academics aim to find a system with well ferromagnetic order,giant spontaneous polarization and high transition temperature above room-temperature.Furthermore,with rapid development of relevant theories and calculation methods,theoretical simulations has paved the way for effective analysis in physics,chemistry and materials science,which could investigate the structures and properties of multiferroic materials from micro-level.The present thesis focuses on the first-principle calculation of multiferroic properties in double perovskite rare earth-nickel-manganse oxides super lattices based on density functional theory with VASP,a software for first principle calculation.Firstly,as R₂NiMnO₆?R represents rare earth elements?ordered superlattice,the thesis calculated four ferromagnetic states,which were FM,A-AFM,G-AFM,C-AFM,respectively.The structure of geometrical ground state for R₂NiMnO₆ was analyzed in detail,while the lattice parameters of the system,such as system basic vector,B-O bond,crystalline condition of BO₆ octahedron as well as relationships of A-site ions,were presented as well.Next,the ferromagnetic Curie temperature was calculated by Monte Carlo method combined with classical Heisenberg models in order to analyze the electronic spins structure and spintronic order of transition metals.Besides,the origin of ferromagnetism was discussed as well.Secondly,multiferroic properties of R₂NiMnO₆/La₂NiMnO₆ordered superlattices were studied in present thesis.The ground states of Pr₂NiMnO₆/La₂NiMnO₆ and La₂Ni MnO₆ were compared in order to analyze the relationship of A-site ionic radius and structural parameters;Next,the ferromagnetic Curie temperature of crystalline lattice was calculated.Meanwhile,the spintronic order of transition metals was analyzed.Moreover,the thesis discussed the origin of ferroelectricity as well as the situation of ions displacement based on Berry phase method,which used to calculate the ferroelectric spontaneous polarization.The relationship between A-site ion radius and ferroelectric polarization was discussed then.Thirdly,Pr₂NiMnO₆/La₂NiMnO₆ nanoparticles were prepared by sol-gel method,while the physical structures and magnetic properties were characterized.At last,the ferromagnetic behaviors and variables for magnetic properties of above metioned nano-samples were analyzed comprehensively.