Polaron Dynamics In Organic Ferromagnets

Organic spin electronics is a new research field.It uses spin freedom of organic materials to develop new functional devices.One of the remarkable characteristics of organic materials different from inorganic materials is that the carriers in conjugated organic molecules are nonlinear excitation,which is due to strong electron lattice interaction.For example,when doping electrons or cavities,polaron excitation can be formed in most degenerate and nondegenerate conjugated polymers.Polaron consists of a unit of charge and spin and localized distortion of the lattice.Under the action of electric field,polaron,as an effective charge / spin carrier,can be transferred in polymer.Therefore,polaron dynamics is an important problem in understanding spin transport in organic spintronics.Organic ferromagnet is a new material which combines the advantages of organic matter and ferromagnet.In experiments,organic ferromagnets can be synthesized by doping transition metal ions(Mn,Fe,Cr or V)or using spin free radicals(heterocycles with unpaired electrons).The latter is a pure organic ferromagnet containing only light elements,such as poly-BIPO,m-PDPC and pyrro-PAN.In recent years,the design of novel organic spin electron devices based on organic magnets has attracted more and more attention.It is of great significance to reveal the nonlinear carrier properties and transport properties in organic magnets.Compared with ordinary polymers,the spin interaction in organic magnets is more complex,which can cause some strange properties of carriers.For example,previous studies have shown that due to the existence of spin free radicals,the polaron charge spin distribution is inconsistent in pure organic ferromagnets.Some researchers have simulated the polaron dynamics in organic ferromagnetism,and reported the spin filtering effect and spin rectification effect.However,the study of polaron dynamics in Organic ferromagnets is still in infancy.Many details of polaron dynamics in Organic ferromagnets is still lacking.For example,In the preliminary work,the polaron dynamics is limited to the spin scattering of a normal polaron suffering to only one spin radical,where the picture is close to the polaron scattering by a local magnetic impurity.In a real OF,the spin radicals are hanged regularly along the whole molecule.The spin-charge relation of the static polaron is distinct from the normal polymer,which is not considered in that work.In addition,spin orbit coupling affects the spin precession period and spin precession length of polaron.However,in the real organic semiconductor materials,it is not only spin orbit coupling that affects the spin precession of polaron.When both effects have influence on the spin precession of polaron,how the spin precession of polaron changes at this time is related work Not considered in.In order to solve the above problems,we use SSH(Su-Schrieffer-Heeger)+ Kondo model to study the polaron characteristics in organic ferromagnets,and further study the polaron dynamic transport in organic ferromagnets,as well as the influence of spin orbit coupling on the polaron dynamic transport.The specific research contents of this paper are as follows:(1)Based on the SSH + Kondo model,we calculated the polaron formation in the ground state of poly-BIPO molecule and doped with one electron,analyzed the characteristics of charge density and spin density of Polaron in static state,and further studied the influence of driving electric field direction,main chain and side group spin correlation strength on the polaron transport velocity in organic ferromagnet in weak field.The results show that due to the existence of spin side groups,the polaron charge density has spatial asymmetry,which leads to different polaron transport velocity in different electric field directions.At the same time,we found that the polaron in the organic ferromagnet will appear "intermittent rebound" this strange phenomenon,and made an explanation.(2)By using the tight binding model and nonadiabatic approximate dynamics method,we study the spin correlation effect and spin orbit coupling effect,the static spin charge characteristics of polaron and its transport properties in the external electric field.The results show that in static state,the spin orbit coupling makes the polaron spin density asymmetric,while the side group spin correlation makes the polaron charge density asymmetric,In the dynamic simulation,it is found that the amplitude and period of the polaron spin precession are changed by the spin orbit coupling effect and the side base spin correlation effect,and there is a competitive relationship between them.