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In metal/oxide heterostructures, rich chemical, electronic, magnetic and mechanical properties can emerge from interfacial chemistry and structure. The possibility to dynamically control interface characteristics with an electric field paves the way towards voltage control of these properties in solid-state devices. Here we show that electrical switching of the interfacial oxidation state allows for voltage control of magnetic properties to an extent never before achieved through conventional magnetoelectric coupling mechanisms. We directly observe, for the first time, in situ voltage driven O$^{2-}$ migration in a Co/metal-oxide bilayer, which we use to toggle the interfacial magnetic anisotropy energy by >0.6 erg/cm$^2$. We exploit the thermally-activated nature of ion migration to dramatically increase the switching efficiency and to demonstrate reversible patterning of magnetic properties through local activation of ionic migration. These results suggest a path towards voltage-programmable materials based on solid-state switching of interface oxygen chemistry.
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Voltage modulation of yttrium iron garnet (YIG) with compactness, high speed response, energy efficiency and both practical/theoretical siginificances can be widely applied to various YIG based spintronics such as spin Hall, spin pumping, spin Seeback effects. Here we initial an ionic modulation of interfacial magnetism process on YIG/Pt bilayer heterostructures, where the Pt capping would influence the ferromagnetic (FMR) field position significantly, and realize a significant magnetism enhancement in bilayer system. A large voltage induced FMR field shifts of 690 Oe has been achieved in YIG (13 nm)/Pt (3 nm) multilayer heterostructures under a small voltage bias of 4.5 V. The remarkable ME tunability comes from voltage induced extra FM ordering in Pt metal layer near the Pt/YIG interface. The first-principle theoretical simulation reveal that the electrostatic doping induced Pt5+ ions have strong magnetic ordering due to uncompensated d orbit electrons. The large voltage control of FMR change pave a foundation towards novel voltage tunable YIG based spintronics.
Ionic liquids (IL) are promising electrolytes for electrochemical applications due to their remarkable stability and high charge density. Molecular dynamics simulations are essential for better understanding the complex phenomena occurring at the electrode-IL interface. In this work, we have studied the interface between graphene and 1-ethyl-3-methyl-imidazolium tetrafluoroborate IL, using density functional theory-based molecular dynamics simulations at variable surface charge densities. We have disassembled the electrical double layer potential drop into two main components: one involving atomic charges and the other - dipoles. The latter component arises due to the electronic polarisation of the surface and is related to concepts hotly debated in the literature, such as the Thomas-Fermi screening length, effective surface charge plane, and quantum capacitance.
The infrared optical, magneto-optical and magnetostrictive properties of CoFe2O4 single crystal are considered. The magneto-transmission and magneto-reflection of natural light in magnetostrictive CoFe2O4 spinel are studied in the Voight experimental geometry. These magneto-optical effects are very high and associate with a change of the fundamental absorption edge and impurity absorption bands under magnetic field. It is presented the effects strongly depend on both the magnitude and orientation of magnetic field relative to the crystallographic axes of the crystal. The clear connection between magneto-absorption of light in the infrared spectral range and magnetostriction of CoFe2O4 spinel is established. The contribution of magnetostriction to the magnetic anisotropy constant of the CoFe2O4 crystal is shown to be abnormally great.
(LaNiO3)n/(LaMnO3)2 superlattices were grown using ozone-assisted molecular beam epitaxy, where LaNiO3 is a paramagnetic metal and LaMnO3 is an antiferromagnetic insulator. The superlattices exhibit excellent crystallinity and interfacial roughness of less than 1 unit cell. X-ray spectroscopy and dichroism measurements indicate that electrons are transferred from the LaMnO3 to the LaNiO3, inducing magnetism in LaNiO3. Magnetotransport measurements reveal a transition from metallic to insulating behavior as the LaNiO3 layer thickness is reduced from 5 unit cells to 2 unit cells and suggest a modulated magnetic structure within LaNiO3.
Solid polymer electrolytes are considered a promising alternative to traditional liquid electrolytes in energy storage applications because of their good mechanical properties, and excellent thermal and chemical stability. A gap, however, still exists in understanding ion transport mechanisms and improving ion transport in solid polymer electrolytes. Therefore, it is crucial to bridge composition--structure and structure--property relationships. Here we demonstrate that size asymmetry, $lambda$, represented by the ratio of counterion to charged monomer size, plays a key role in both the nanostructure and in the ionic dynamics. More specifically, when the nanostructure is modified by the external electric field such that the mobility cannot be described by linear response theory, two situations arise. The ionic mobility increases as $lambda$ decreases (small counterions) in the weak electrostatics (high dielectric constant) regime. Whereas in systems with strong electrostatic interactions, ionomers with higher size symmetry ($lambda approx 1$) display higher ionic mobility. Moreover, ion transport is found to be dominated by the hopping of the ions and not by moving ionic clusters (also known as vehicular charge transport). These results serve as a guide for designing ion-containing polymers for ion transport related applications.
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