Magnetic Resonance And Spin Current At Magnetic Interface

Spin precession and the interaction with spin current at the magnetic interface are the key physical issues in spintronic logic and memory devices.Commercial devices such as magnetic random access memory and magnetic sensors have been realized based on numerous spin-related effects in ferromagnetic materials,such as pure spin current,spin Hall effect,spin transfer torque,magnetoresistance,spin precession,etc.With the increasing requirements of device miniaturization,there are two important research directions in spintronics:1.Excitation,detection and manipulation of magnons and spin currents at the interface of magnetic materials.2.Spin precession and the interaction with spin currents in antiferromagnets with terahertz spin dynamics frequencies and zero stray fields.The challenges in developing the next-generation spintronics devices include 1.New manipulation technology on magnon and spin current is needed to avoid the defects and the reduced spin coherence length in magnetic materials induced by the interface structure design and material doping.2.Excitation and detection of magnons in antiferromagnets with terahertz spin-dynamic frequencies and zero net magnetization require higher frequency excitation means and higher external magnetic fields,improving the difficulty in studying antiferromagnetic spindynamics.In this work,we focused on the ferrimagnetic YIG and antiferromagnetic CrCl3/heavy metal Pt heterojunctions and studied three key issues at the magnetic interface:the magnetization coupling,the excitation and detection of the magnon,and the magnon-driven spin current.We clarified the magnetization coupling,the charge density modulated spin pumping,and the antiferromagnetic spindynamics and antiferromagnetic spin pumping at the GGG/YIG/Pt and CrCl3/Pt interface,which provided a new method for manipulating the magnon and spin current.The main work is as follows:1.We studied the magnon dispersion shift in YIG induced by antiferromagnetic coupling at the GGG/YIG interface,and developed a method to control magnon dispersion,intensity,and linewidth information by using antiferromagnetic coupling.We described the experimental observation by an antiferromagnetic-type interaction between MYIG and MGGG in the Landau-Lifshitz-Gilbert equation.Accordingly,we found that the antiferromagnetic coupling effective field can be enhanced by increasing the magnetic field or by decreasing the temperature,and this finding was confirmed by experimental results.This provided a new method for manipulating the magnon.Additionally,in a van der Waals antiferromagnetic CrCl3,we investigated the sublattice magnetizations angle-dependent acoustically and optically resonance amplitude.We found that the acoustical mode resonance amplitude was strongest when the sublattice magnetizations are parallel.But the optical mode resonance amplitude was strongest when the sublattice magnetizations are anti-parallel.These results suggest that the optical mode is more related to the Neel vector,which is different from that the acoustic mode and the ferromagnetic Kittel mode are more related to the net magnetization.2.We studied the manipulation of spin pumping and spin current transport by the charge density at the YIG/Pt interface,and found a linear dependence between the resonance linewidth characterized interface spin mixing conductance and the interface charge density,which is helpful for understanding spin transport at ferromagnetic/heavy metal interfaces.In experiments,we used the gate voltage technology to control the charge density in the Pt layer,and the tunable spin mixing conductance up to 22%.We quantitatively described the experimental measured inverse spin Hall voltage by considering the gate voltage dependent magnetic resonance damping,spin mixing conductance,and resistance of the Pt layer.We found that the spin Hall angle in the Pt layer is also modulated by the charge density,with a change rate of ±13.6%.These results confirmed the possibility of electrical control of the interfacial spin current by adjusting the interfacial charge density in the ferromagnetic/nonmagnetic bilayer.3.We studied the acoustic and optical mode-driven spin currents in CrCl3/Pt,and confirm that the optical mode-driven spin currents come from the processing Néel vector.We detected the inverse spin Hall voltage induced by the spin current in the directions parallel and perpendicular to the external magnetic field,respectively,and the results showed that the spin current has only a spin-polarized component parallel to the external magnetic field.In addition,we studied the change of the spin current intensity with the angle of the magnetic moment of the sublattice.We found that when the relative angle of the magnetic moment of the sublattice was reduced from the antiparallel state to the parallel state,the acoustic mode spin current amplitude gradually increases,which is due to the spin current of the acoustic mode being driven by the net magnetic moment vector.The optical mode spin current intensity increases first and then decreases with the decrease of the sublattice magnetizations angle.We confirm that this is due to the optical mode spin current being driven by the Néel vector,and the net magnetic moment does not contribute to the spin current.This is the first direct observation of optical mode driven spin current in experiments,confirming the unique role of the Neel vector in antiferromagnetic spindynamics.