Characterization,Modulation,and Application Of Interface-related Properties In Magnetic Films With Heterostructure

As core materials for application in spintronics,nano-scaled magnetic films with heterostructure are closely related to the surface/interface effect.In this thesis,we focus on studying the role of heterogeneous interface(such as Oxide/Ferromagnetic Metal or Ferromagnetic Metal/Heavy Metal)in magnetic properties and spin-dependent transport.Firstly,experimental measurements and characterizations show that interface structures and chemical states are correlated with material properties.Secondly,by elaborate modulation of interface structures,the related material properties are modified.Finally,novel spin logic applications of magnetic multilayers with heterostructure are developed.Primary contents and results are as follow:(1)Epitaxial L10-FePt/MgO/L10-FePt magnetic tunnel j unctions with perpendicular magnetic anisotropy were fabricated.Based on the results from first-principles calculation and interfacial characterization,the role of Pt-or Fe-terminated layer at the FePt/MgO interface on spin-dependent tunneling is clarified.(2)The effect of middle Fe thickness on tunneling behavior in epitaxial Fe/MgO/Fe/MgO/Fe magnetic tunnel junctions was studied by temperature-and bias-voltage-dependent transport measurements.The morphology of middle Fe layer and interface structure of MgO/Fe/MgO were in situ characterized by transmission electron microscopy at atomic resolution.Based on both results,the evolution of interface structure plays an important role in tuning transport channels,leading to the change of tunneling behavior.(3)In three typical material systems including disordered FePt film,[Pt/Co]3/MgO multilayers and Ta/CoFeB/MgO/Ta multilayers,magnetic and transport properties were modulated by tuning the chemical states at Oxide/Ferromagnetic Metal interface:By sandwiching ultrathin disordered FePt film with chemically stable SiO2 layers,the interfacial perpendicular magnetic anisotropy was enhanced.By inserting a Ta layer with optimized thickness at Co/MgO interface,thermally stable(450 ℃)perpendicular magnetic anisotropy and large anomalous Hall signal were obtained simultaneously in[Pt/Co]3/Ta/MgO.By inserting a Gd layer with strong oxygen affinity at CoFeB/MgO interface,the effective damping constant of Ta/CoFeB/Gd/MgO/Ta was greatly reduced by 70%while the perpendicular magnetic anisotropy can be maintained.(4)Based on the spin-orbit torque switching mechanism,all 16 Boolean logic functions were experimentally realized in Ta/CoFeB/MgO/Ta multilayers with perpendicular magnetic anisotropy.Furthermore,utilizing both the spin-orbit torque switching and voltage-controlled magnetic anisotropy,a three terminal spin logic cell was designed.Simulation results show that all 16 Boolean logic functions can be fast operated in a single cell.Based on this idea,logic functions independent of magnetic field can be realized in practical devices by optimizing material structures.This work might pave the way for the fusion of processing and nonvolatile memory units in the future integrated circuits,and will break the development bottleneck in the current CMOS technology and von Neumann architecture.