The Magnetoelectric Transport Properties And Spin Dynamics At The Oxide Interfaces

Due to the interplay between charge,orbital,spin,and lattice degrees of freedom,oxide interfaces have shown an incredible variety of physical phenomena,including quantum phase transition between an insulating,superconducting,and metallic ground state with the modulation of carrier density by applying an external electric field.In this thesis,we focus ourselves on the effects of applied electric field,temperature gradient,and laser pulse on the magnetoelectric transport properties and spin dynamics at the oxide interfaces.We unravel a new and highly efficient way of non-magnetic control of spin accumulation and spin transport in the two-dimensional electron gas at the helimagnetic oxide interface,and theoretically investigated the ultrafast transient dynamics of coupled ferroelectric/ferromagnetic composites dominated by the interface multiferroic interaction.These findings would have a great influence on the development of multi-field-controllable spintronic devices based on the oxide interfaces with novel functionalities and low energy consumptions.In chapter 1,we review what is known about the magnetoelectric transport properties and spin dynamics at the oxide interfaces,including the generation of two dimensional gases,spin-orbit effects,spin transfer torque and corresponding emergent phenomena.In chapter 2,we investigate the giant spin-orbit torque and spin current generation in carriers at oxide interfaces.Interfacing polar insulating oxides may result in the formation of interface-confined,high density carriers and high mobility with a number of emergent properties.A local coupling of carriers to a helimagnetic oxide layer is shown to lead to an effective spin-orbit interaction with a band splitting determined by the local s-d exchange interaction.As a result,a non-equilibrium long-lived spin accumulation normal to the spiral plane induced by the electric field or the temperature gradient is predicted.In particular,we find that the spin accumulation is strongly enhanced by 2or 3 orders of magnitude as only one of the two bands is at the Fermi level and the chemical potential is close to the band edge.As a consequence we predict a large spin transfer torque and spin current emission that can be utilized for oxide-based spintronic applications.In chapter 3,we investigate the transport properties of the oxide interfaces with anisotropic spin-orbit coupling.Considering the two-dimensional electron gases with a transverse spiral magnetic order at the oxide interfaces,Rashaba spin-obit interaction competes with the induced gauge spin-orbit interaction linear to the helicity of magnetic order.Both of the two spin-orbit interaction can be modulated by the electric field.As a result,the system has an electrically controlled anisotropic spin-orbit coupling.Then we analyze how the anisotropic spin-orbit coupling affects the transport properties,such as the Seebeck effect and the spin Seebeck effect at the longitudinal direction,the Hall effect,the spin Hall effect,and the thermal Hall effect at the transverse direction.In chapter 4,we investigate the ultrafast transient dynamic multiferroic response of interface coupled ferroelectric/ferromagnetic composites upon excitation by a photoinduced acoustic strain pulse.Two magnetoelectric mechanisms are considered: interface strain-and charge-mediated magnetoelectric couplings.The former results in demagnetization,depolarization and repolarization within tens of picoseconds via respectively magnetostriction and piezoelectricity.Charge magnetoelectric interaction affects the ferroelectric/ferromagnetic feedback response leading to magnetization recovery.Experimental realization based on time-resolved x-ray diffraction is suggested.These findings are exciting and useful for realizing low energy cost,high frequency oxide-based spintronic applications and photo-steered,high-speed,multi-state composite multiferroic electronic devices.At last we summarize the thesis and provide an outlook of the future study in Chapter 5.