| Data storage and logical operation are the foundation of today’s information age.With the popularization of 5G communication technology and the development in the field of big data,artificial intelligence,etc.,people’s demand for high-density,energy-efficient,high-speed memory is surging.Magnetic random access memory(MRAM)on the basis of the spin property of electrons is one of the most promising candidates for the next generation of high-efficiency storage technology.Therefore,rich spintronic phenomena such as anisotropy magnetoresistance,giant magnetoresistive effect,Hall effect family,Rashba effect,spin thermoelectric effect,and multiferroic have successively become the focus of researchers.Moreover,the realization of the control of magnetism makes these spintronic phenomena be regulated to be expected,among which electrical regulation of magnetism is the most effective way to achieve reversible and non-volatile control of magnetic anisotropy and magnetic ordering under low-energy consumption,and also meets the design demand of highly integrated devices compatible with semiconductor processes.In the strongly correlated oxides system,the four degrees of freedom of lattice,charge,spin,and orbit are highly interrelated,and the coupling between the different degrees of freedom produces a variety of physical and chemical properties,which provides a basis for exploring interesting physical effects and phenomena in spintronics,and also provides a huge arena for the design and improvement of high-performance memory devices.In this dissertation,the properties of electric field control of magnetism as well as electron transportation will be studied from some ion-based and manganese-based strongly correlated oxide systems.The large interfacial electric field induced by the ionic liquid electric double layer enables ion migration in the system,which has a critical effect on the lattice periodic potential field,charge filling,orbital occupancy,and spin polarization.However,the ion migration in this mode will be accompanied by the reverse movement of the oppositely charged ions,which is not conducive to stable physical phenomena and a clean physical mechanism.Two-dimensional graphene could serve as an ion sieve,thus allowing only protons rather than oxygen ions or other groups to participate in the gating process.When H+ migrates reversibly in the Fe3O4/graphene system at the ionic liquid electric field,the magnetic anisotropy,magnetoresistance,and saturation magnetization of Fe3O4 could be manipulated reversibly and non-volatile.The charge of crystal structure and valance state of Fe3O4 induced by proton’s migration are analyzed by X-ray diffraction,X-ray photoelectron spectroscopy,and secondary ion mass spectrometry,moreover,the mechanism of proton’s intercalation on the magnetic structure of Fe3O4 is clarified by density functional theory,thus provides a new idea for the study of selective ion migration in the functional strongly correlated system.In addition,two-dimensional magnetic materials have great application potential in the field of wearable artificial intelligence,and graphene is one of the most classical two-dimensional materials with high carrier mobility and structural flexibility.This paper uses mechanical folding and successive rapid heating and cooling to achieve a robust ferromagnetic order in the few-layer graphene with a Curie temperature of more than 100 K,which is essential for graphene in the future of flexible electronic materials,such as storage and artificial intelligence.Spin orbit torque(SOT)on the basis of spin-orbit coupling(SOC)has become a research hotspot due to its advantages of read-write split electric-control-of magnetism,high efficiency,and compatibility with integrated circuits.How to improve SOT efficiency has become the focus of researchers,in addition to alloying,structural intercalation,interface oxidation,etc.,it will be very meaningful and valuable to study how to improve SOC and SOT efficiency from the orbital degree of freedom.In the W3O8-δ/LSMO heterostructure,the insulator-to-metal transition is realized by extracting oxygen ions from W3O8-δ layer at the ionic liquid electric field,and the spin Hall effect derived from the intrinsic SOC of the W3O8-δ as well as the Rashba-Edelstein effect caused by the interfacial inversion asymmetry of W3O8-δ/LSMO enables a charge-to-spin current transition and SOTs.As a result,the spin Hall magnetoresistance could be reversibly controlled by an electric field;magnetization switching has been realized by exerting SOTs on the ferromagnetic LSMO layer,and the damping-like/field-like effective fields and spin Hall angle have been quantitatively analyzed by the second harmonic method.By introducing strain engineering through changing the substrate,control of the orbital occupancy state of W-5d/Mn-eg electrons is realized,and then the spin Hall effect of bulk WO3-δ as well as the interfacial Rashba SOC of W3O8-δ/LSMO are regulated,and finally,the SOT efficiency enhancement is achieved by the orbital regulation.This provides the basis for orbit occupancy engineering the SOC and SOT efficiency as well as studying their physical mechanism.The transition between Fe2+ and Fe3+ in ion-based oxides is often accompanied by changes in spin textures and electron transportation properties.In this work,a shell layer of the Fe3O4 phase is obtained on the surface of α-Fe2O3 by vacuum annealing,and theα-Fe2O3/Fe3O4 structure with interfaces is formed by breaking the inversion symmetry due to a structural change of the surface crystal.The oxygen ions at the interface could migrate almost reversibly under the electric field,and the magnetic moments of α-Fe2O3/Fe3O4 as well as the exchange bias fields could be reversibly regulated.These results provide support for the study of magnetic physics and electric control of magnetism under the mechanism of oxygen vacancy migration.In the scenario that the 180° magnetization switching is only possible in very limited systems,and spin transfer torque(STT)technology requires a large current density(>105 A/cm2)although it can freely switch the magnetic moments,the inevitable Joule heat induced by current will have a crucial bearing on the device tolerance and stability.In the ferrimagnetic garnet Dy3Fe5O12 and Tb3Fe5O12,the unique magnetic moment compensation and angular momentum compensation mechanisms make the magnetic structure very sensitive to temperature variation.A temperature elevation of several Kelvin could be achieved with a very low current density(10-3A/cm2),and this temperature change,which stretches across the compensation temperature,can achieve a macroscopic 180°magnetization switching by locally changing the contribution of sublattice magnetic moments.In this section,the changes in magnetic ordering structure affected by Joule heat are systematically studied,and the magnetization switching at low current density is realized,which provides help for thermally assisted magnetization switching. |
PDF Full Text Request