Phenomenological Studies On Two Dimensional Ferroelectric Models And Multiferroic Skyrmion Lattice

Ferroelectric materials refer to the kind of materials that has spontaneous polarization which can reverse under the stimulations of external electric field.Because of such a nature,ferroelectric materials have been a hot research topic for decades,especially in nowadays,when computer and communication technologies are under rapid development.Ferroelectric materials,because of their abundant application prospects,obtained continuous attentions from researchers,while multiferroic materials coming into the sights of people recently made the traditional ferroelectric physics to glow with new vitality.One of the main applications of ferroelectricity is to utilize its nature of dipole-switching under external electric field to realize convenient and reliable information storage as well as other related applications in microelectronic industy.Therefore,the mechanisms of ferroelectric polarization reversal are very important.On the other hand,various domain structures of ferroelectric materials under different conditions are of great importance for the ferroelectric applications.In fact,people name ferroelectric materials as functional materials,in some extent,just because of their abundant domain patterns.Except for traditional ferroelectric materials,single-phase multiferroic materials intrigued lots of researchers for the prospects of electric control of magnetic states and vice versa,which may enable more microelectric applications.For the above reasons,our studies are focused on three aspects of ferroelectrics:(1)dynamics of hysteresis of a two dimensional ferroelectric model,(2)domain patterns of two dimensional ferroelectric nanoislands,and(3)dielectric responses of improper ferroelectric induced by the inverse DM interactions of magnetic spins.The methods we used for the studies are phenomenological approachs,including Monte Carlo and phase field simulations.In the first area of our study,we put a square lattice of dipoles under external altenate electrical fields,and found double-peak behaviors in area-frequecy(A(ω)～ω)curves,which are different from previous studies.We also found the power law scaling behaviors still applicable in the two directions of low and high frequencies.In the model ferroelctric nanoislands,we investigated domain patterns of the islands under different conditions including various sizes of nanoislands,different magnitudes and signs of defect charges in the islands.We found that the sizes of nanoislands,the magnitudes and signs of electric charge defects affected structures and symmetries of ferroelectric domains collaboratively.In the third study of multiferroic skyrmion lattice,we applied electric fields inside the xy plane,then along the z axis.Under the two stimuli,we investigated the dielectric responses of the dipole skyrmion lattice,and observed some interesting dielectric response patterns as well as some intriguing physics.