Interfacial Magnetoelectric Dynamics

Due to rapid development of micro-nano devices and more and more serious heatgenerating problem of electric current,traditional electronic devices,which only use the charge nature of electron,have not met our needs of ultra-low power consumption and exact localization.The spin nature of electron is introduced to explore new devices with advantages of spin and charge natures.Traditionally,we use a magnetic field,which is generated by electric current,to control the spin.Heat loss of electric current and inherent non-locality of magnetic field become major hindrances on that road.A possible work-around is the use of electric field as a switching tool to manipulate spin.It is possible to control the magnetism with electric field in multiferroic materials because the electricity and magnetism coexist and in particular magnetoelectric coupling occurs in ones.Miniaturization,low dimension and artificial complex materials make the surface and interface more and more important.Interfacial magnetoelectric coupling becomes a research focus.According to the magnetoelectric coupling effect in multiferroic system,we have made a series of investigations on the interfacial magnetoelectric coupling effect in ferromagnetic metal interface system and insulator interface system and their possible origins in my dissertation theoretically.Then introduce two mechanisms about the interfacial magnetoelectric coupling,which are spin screening charge mechanism in ferromagnetic metal system and Peierls mechanism in insulator system respectively.In ferromagnetic metal system,the magnetoelectric coupling effect originates from the inhomogeneous spin texture induced by screening charge.The adiabatic part of induced spin,which is along the direction of the local magnetic moment,would introduce a static magnetoelectric coupling.And the non-adiabatic part,which describes the transverse deviation from local magnetic moment,could have effect on the magnetic dynamics of local magnetic moment by use of Landau-Lifshitz-Baryakhtar equation(LLBar equation).From magnetic dynamics,we have a flip of magnetic moment in a suitable applied electric field.In insulator system,a dynamic magnetoelectric coupling effect occurs due to internal and external electric field coupling with Peierls mechanism.Via the linear dynamic magnetoelectric coupling,the effective magnetic susceptibility will be dependent on an applied electric field.And especially a negative magnetic susceptibility could be obtained by tuning electric field.In addition when there are a huge magnetoelectric coupling and a small enough relative dielectric constant,we can get a negative refractive index.In insulator system,the anti-ferromagnetic insulator system has more complex internal electric field because spin of conduction electron cannot be along the direction of the defined order parameter under adiabatic approximation due to the rapid flip of adjacent local spins.The magnetoelectric coefficient is dependent on time,which is very different from the independent one in ferromagnetic insulator system.Importantly,that there is an effective transformable magnetic susceptibility with a linear magnetoelectric coupling is universal in insulator interface system and metal interface system and even in bulk materials.