Study On The Mechanism Of Electric Field Control Magnetism Of Transition Metal Oxide Magnetic Materials

Electric field control of magnetism has become an attractive research field due to its low power consumption,high speed,reversibility,non-volatility and good compatibility with the traditional semiconductor industry.In the field of spintronics and energy storage,the coupling based on magnetic field and electric field has attracted much attention.Spintronics uses the spin and magnetic moment of electrons to realize the mutual regulation between charge transport and magnetism.Electrochemical energy storage is to manipulate and store charge through electrochemical reaction.Therefore,they are essentially manipulating electrons.The idea of magnetoelectric coupling in spintronics provides a new idea for the study of electrochemical mechanism,so that we can analyze the electrochemical reaction mechanism from the perspective of magnetism.Combining the fields of magnetism and electrochemistry,based on the principle and technology of electrochemistry,using advanced in-situ physical property measurement system,we can monitor the dynamic information of charge transport,structural change and magnetic response in electrochemical reaction in real time,and obtain information that other traditional theoretical techniques cannot obtain,which has become a powerful tool for studying the mechanism of magnetoelectric regulation.Transition metal oxide materials are widely used in spintronic devices and electrochemical energy storage due to their unique electronic structure and magnetic properties,which lays a foundation for the application of magnetic testing in magnetism and electrochemistry.Therefore,the combination of magnetic theory and in-situ magnetic testing technology not only helps to study the change mechanism of structural phase transition and local electron distribution in transition metal oxide energy storage materials,but also helps us analyze the electrochemical reaction mechanism from a more essential perspective,and uses electrochemical reaction to regulate magnetism,which provides new ideas for the design of magnetic control devices.In this paper,the relationship between the structural and magnetic changes of transition metal oxide magnetic materials was analyzed by operando magnetometry,and the mechanism of electric field regulating magnetic properties was systematically studied.The main contents include the following three parts:1.Revealing the electrochemical regulation mechanism of Ni Fe₂O₄ lithium-ion batteries by operando magnetometry.During the insertion reaction phase,keeping the structure intact,the electric field drives ion migration leading to valence state changes and partial redistribution of Fe³⁺cations,thus producing a reversible change in magnetization at room temperature with an amplitude of approximately 0.6 emu g^?1.In the low voltage spin capacitance range,nano-scale Ni⁰/Fe⁰ and Li₂O were obtained by electrochemical reduction to 0.01 V.Then,on the premise of avoiding the oxidation of Ni⁰/Fe⁰,the reversible regulation of the saturation magnetization of the ferromagnet are achieved by Li ion motion across the ferromagnet/lithionic conductor interfaces.At the same time,the regulation mechanism of magnetic changes was verified by a series of ex-situ structural and physicochemical characterization tests.This provides a new method for studying the internal reaction mechanism of spinel magnetic materials.2.Revealing the electrochemical regulation mechanism of Zn Fe₂O₄ lithium-ion batteries by operando magnetometry.Following the same idea,we chose the spinel structure Zn Fe₂O₄as the object of further study.By operando magnetometry,it was found that Zn Fe₂O₄ lithium-ion batteries also experienced insertion reaction and spin capacitance,and compared with Ni Fe₂O₄,the magnetic change amplitude was greater,5.6 emu g^?1 and 3 emu g^?1,respectively.Although the selected voltage intervals are slightly different,stable and reversible magnetic regulation can be achieved based on both reaction mechanisms.These important results not only provide a new idea for the large-scale and highly reversible regulation of bulk materials,but also open the door for the regulation of transition metal oxide magnetic materials,paving the way for the development of ion-based magnetoelectric coupling applications.3.Revealing the electrochemical regulation mechanism of Fe₂O₃@Ti O₂ lithium-ion batteries by operando magnetometry.The Fe₂O₃@Ti O₂ was reduced to a nanoscale Fe⁰/Li₂O mixture by the reaction principle of lithium-ion batteries,and since Ti O₂ does not produce magnetic changes during the reversible insertion of lithium ions,the magnetic change of the Fe₂O₃@Ti O₂ is due to the redox reaction of Fe₂O₃ and the spin capacitance formed at the Fe⁰/Li₂O interface.The operando magnetometry shows that the reversible regulation of the saturation magnetization intensity of the ferromagnet can be achieved by the movement of lithium ions at the ferromagnetic/lithium-ion conductor interfaces,and the amplitude change is about 8 emu g^–1.At the same time,under the premise of avoiding the occurrence of spin capacitance,when discharged to 0.7 V,Fe₂O₃ is reduced to metal Fe⁰.When charged to 3.0 V,it does not return to its original state,but has obvious magnetic properties.Through the characterization of ex situ structure,physicochemical properties,we confirmed that Fe⁰ is oxidized to Fe O.This lays a theoretical foundation for the study of interfacial magnetism of transition metal oxide heterojunctions.