Reversible Control Of The Magnetization Of Spinel Ferrites Based Electrodes Via Lithium Ions

Electric-field control of magnetization has attracted intensive research interests in recent years for its potential applications in magnetic memory storage,sensors,and spintronics.The magnetoelectric coupling could be generally divided into three kinds:strain-mediated magnetoelectric coupling,charge-mediated magnetoelectric coupling,and magnetoelectric coupling in multiferroic materials.Both magnetic control of ferroelectric polarization and electric control of magnetization have been demonstrated in some artificially structured composites by varieties of methods.However,traditional electric control methods generally operate in a few atomic layers adjacent to the surface or the interface,and conventional magnetoelectric couplings are weak in most cases.As a result,various efforts have been made to find an alternative approach to improve the effectiveness.The electrochemical control of magnetism has been intensively investigated in materials with multiple functionalities.Recently,researchers have also focused on the coexistence of magnetism and ion storage ability in transition metal oxides which have been widely explored for high-performance lithium ion batteries.It is worth noting that the redox states of these materials can be controlled by the electrochemical process.Since the variation of the valence state in transition metal may alter the magnetically related d orbital electrons,a reversible control of magnetism could be realized if the charge/discharge voltage range is carefully set.As the storage of lithium is a bulk behavior in these materials,the magnetic response to electrical stimulus could go beyond the surface reaching a large change magnitude.This brilliant feature,advanced by the rapid development of lithium battery manufacturing technique,makes it also a promising approach to achieve a magnetism modulation.In this work,an in situ magnetic measurement of Fe₃O₄ nano-particles and NiFe₂O₄ hollow porous nanoboxes during the inserting/extracting of Li ions using a miniature lithium-battery?LIB?cell was made.The cycling time are both around 10 min and can be further reduced if a higher current density is applied.In the meantime,we tried to understand the modulation mechanism using different characterization methods,and found some other factors influencing the magnetic response in the modulation process apart from the valence change.In order to find out what these factors are,we made a series of research on spinel MnFe₂O₄ and ?-Fe2O3 electrode.The electrochemical reaction process was investigated from the early beginning of Li uptake to the full conversion of the anode into rock-salt structure.In combination with a variety of complementary analytical tools used to probe the structural,electronic and chemical changes,reaction mechanism involved with the battery operation and ferromagnetism change is established.In order to overcome the drawbacks of liquid electrolyte such as leakage risk and bad stability,an all solid-state film lithium battery is demonstrated,which reveals an obvious change of magnetization during the ion migration process.Inverse spinel structured Fe₃O₄ was selected in this work due to its low activation energies for Li+ion migration.LiCoO₂ is chosen to be the counter electrode as the external Li+ ions source to compensate for Li loss in the electrolyte.A commercial LISICON(Li_1.5Al_0.5Ge_1.5P₃O₁₂)ceramic plate with a thickness of 0.3mm is used as the electrolyte to achieve a quick transport of Li+ ions.The saturation magnetization of the device shows two distinct magnetic values in the charged/discharged states.The research of this article has broad application prospects both in the fabrication of new electronic devices and the development of new energy materials.