Ferrimagnetic Heusler tunnel junctions with fast spin-transfer torque switching enabled by low magnetization.

Magnetic random-access memory that uses magnetic tunnel junction memory cells is a high-performance, non-volatile memory technology that goes beyond traditional charge-based memories. Today, its speed is limited by the high magnetization of the memory storage layer. Here we prepare magnetic tunnel junction memory devices with a low magnetization ferrimagnetic Heusler alloy MnGe as the memory storage layer on technologically relevant amorphous substrates using a combination of a nitride seed layer and a chemical templating layer.

Heusler-based synthetic antiferrimagnets.

Antiferromagnet spintronic devices eliminate or mitigate long-range dipolar fields, thereby promising ultrafast operation. For spin transport electronics, one of the most successful strategies is the creation of metallic synthetic antiferromagnets, which, to date, have largely been formed from transition metals and their alloys. Here, we show that synthetic antiferrimagnetic sandwiches can be formed using exchange coupling spacer layers composed of atomically ordered RuAl layers and ultrathin, perpendicularly magnetized, tetragonal ferrimagnetic Heusler layers.

Proteomic and metabolomic approach to rationalize the differential mosquito larvicidal toxicity in sp. isolated from the mid-gut of mosquito larvae.

From the distinct wild locations of the Mumbai (India), dead Culex mosquito larvae were collected. The mid-gut micro-flora of these dead mosquito larvae was isolated on three different media that were selective for only the Gram-positive bacteria. These bacteria were tested against the third instar stage of larvae, cultured in the laboratory, for their larvicidal activity.

Nonlinear Magnetization Dynamics Driven by Strong Terahertz Fields.

We present a comprehensive experimental and numerical study of magnetization dynamics in a thin metallic film triggered by single-cycle terahertz pulses of ∼20  MV/m electric field amplitude and ∼1  ps duration. The experimental dynamics is probed using the femtosecond magneto-optical Kerr effect, and it is reproduced numerically using macrospin simulations. The magnetization dynamics can be decomposed in three distinct processes: a coherent precession of the magnetization around the terahertz magnetic field, an ultrafast demagnetization that suddenly changes the anisotropy of the film, and a uniform precession around the equilibrium effective field that is relaxed on the nanosecond time scale, consistent with a Gilbert damping process.

Fast Spiking of a Mott VO-Carbon Nanotube Composite Device.

The recent surge of interest in brain-inspired computing and power-efficient electronics has dramatically bolstered development of computation and communication using neuron-like spiking signals. Devices that can produce rapid and energy-efficient spiking could significantly advance these applications. Here we demonstrate direct current or voltage-driven periodic spiking with sub-20 ns pulse widths from a single device composed of a thin VO film with a metallic carbon nanotube as a nanoscale heater, without using an external capacitor.

Localized Triggering of the Insulator-Metal Transition in VO Using a Single Carbon Nanotube.

Vanadium dioxide (VO) has been widely studied for its rich physics and potential applications, undergoing a prominent insulator-metal transition (IMT) near room temperature. The transition mechanism remains highly debated, and little is known about the IMT at nanoscale dimensions. To shed light on this problem, here we use ∼1 nm-wide carbon nanotube (CNT) heaters to trigger the IMT in VO.

Flat Monolayer Graphene Cathodes for Li-Oxygen Microbatteries.

Miniature batteries can accelerate the development of mobile electronics by providing sufficient energy to power small devices. Typical microbatteries commonly use thin-film inorganic electrodes based on Li-ion insertion reaction. However, they rely on the complicated thin-film synthesis method of inorganics containing many elements.

Chiral domain wall motion in unit-cell thick perpendicularly magnetized Heusler films prepared by chemical templating.

Heusler alloys are a large family of compounds with complex and tunable magnetic properties, intimately connected to the atomic scale ordering of their constituent elements. We show that using a chemical templating technique of atomically ordered X'Z' (X' = Co; Z' = Al, Ga, Ge, Sn) underlayers, we can achieve near bulk-like magnetic properties in tetragonally distorted Heusler films, even at room temperature. Excellent perpendicular magnetic anisotropy is found in ferrimagnetic XZ (X = Mn; Z = Ge, Sn, Sb) films, just 1 or 2 unit-cells thick.

Evidence for Ionic Liquid Gate-Induced Metallization of Vanadium Dioxide Bars over Micron Length Scales.

It has recently been shown that the metal-insulator transition in vanadium dioxide epitaxial films can be suppressed and the material made metallic to low temperatures by ionic liquid gating due to migration of oxygen. The gating is only possible on certain crystal facets where volume channels along the VO's rutile c-axis intersect the surface. Here, we fabricate bars with the c-axis in plane and oriented parallel to or perpendicular to the length of the bars.

Reversible Formation of 2D Electron Gas at the LaFeO /SrTiO Interface via Control of Oxygen Vacancies.

A conducting 2D electron gas (2DEG) is formed at the interface between epitaxial LaFeO layers >3 unit cells thick and the surface of SrTiO single crystals. The 2DEG is exquisitely sensitive to cation intermixing and oxygen nonstoichiometry. It is shown that the latter thus allows the controllable formation of the 2DEG via ionic liquid gating, thereby forming a nonvolatile switch.

Transparent conducting oxide induced by liquid electrolyte gating.

Optically transparent conducting materials are essential in modern technology. These materials are used as electrodes in displays, photovoltaic cells, and touchscreens; they are also used in energy-conserving windows to reflect the infrared spectrum. The most ubiquitous transparent conducting material is tin-doped indium oxide (ITO), a wide-gap oxide whose conductivity is ascribed to n-type chemical doping.

Metallization of Epitaxial VO2 Films by Ionic Liquid Gating through Initially Insulating TiO2 Layers.

Ionic liquid gating has been shown to metallize initially insulating layers formed from several different oxide materials. Of these vanadium dioxide (VO2) is of especial interest because it itself is metallic at temperatures above its metal-insulator transition. Recent studies have shown that the mechanism of ionic liquid gated induced metallization is entirely distinct from that of the thermally driven metal-insulator transition and is derived from oxygen migration through volume channels along the (001) direction of the rutile structure of VO2.

Facet-Independent Electric-Field-Induced Volume Metallization of Tungsten Trioxide Films.

Reversible metallization of band and Mott insulators by ionic-liquid gating is accompanied by significant structural changes. A change in conductivity of seven orders of magnitude at room temperature is found in epitaxial films of WO3 with an associated monoclinic-to-cubic structural reorganization. The migration of oxygen ions along open volume channels is the underlying mechanism.

Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy.

Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition.

Termination layer compensated tunnelling magnetoresistance in ferrimagnetic Heusler compounds with high perpendicular magnetic anisotropy.

Although high-tunnelling spin polarization has been observed in soft, ferromagnetic, and predicted for hard, ferrimagnetic Heusler materials, there has been no experimental observation to date of high-tunnelling magnetoresistance in the latter. Here we report the preparation of highly textured, polycrystalline Mn3Ge films on amorphous substrates, with very high magnetic anisotropy fields exceeding 7 T, making them technologically relevant. However, the small and negative tunnelling magnetoresistance that we find is attributed to predominant tunnelling from the lower moment Mn-Ge termination layers that are oppositely magnetized to the higher moment Mn-Mn layers.

Broadband extreme ultraviolet probing of transient gratings in vanadium dioxide.

Nonlinear spectroscopy in the extreme ultraviolet (EUV) and soft x-ray spectral range offers the opportunity for element selective probing of ultrafast dynamics using core-valence transitions (Mukamel et al., Acc. Chem.

Giant reversible, facet-dependent, structural changes in a correlated-electron insulator induced by ionic liquid gating.

The use of electric fields to alter the conductivity of correlated electron oxides is a powerful tool to probe their fundamental nature as well as for the possibility of developing novel electronic devices. Vanadium dioxide (VO2) is an archetypical correlated electron system that displays a temperature-controlled insulating to metal phase transition near room temperature. Recently, ionic liquid gating, which allows for very high electric fields, has been shown to induce a metallic state to low temperatures in the insulating phase of epitaxially grown thin films of VO2.

Distinct electronic structure of the electrolyte gate-induced conducting phase in vanadium dioxide revealed by high-energy photoelectron spectroscopy.

The development of new phases of matter at oxide interfaces and surfaces by extrinsic electric fields is of considerable significance both scientifically and technologically. Vanadium dioxide (VO2), a strongly correlated material, exhibits a temperature-driven metal-to-insulator transition, which is accompanied by a structural transformation from rutile (high-temperature metallic phase) to monoclinic (low-temperature insulator phase). Recently, it was discovered that a low-temperature conducting state emerges in VO2 thin films upon gating with a liquid electrolyte.

Subnanosecond incubation times for electric-field-induced metallization of a correlated electron oxide.

Strong interactions, or correlations, between the d or f electrons in transition-metal oxides lead to various types of metal-insulator transitions that can be triggered by external parameters such as temperature, pressure, doping, magnetic fields and electric fields. Electric-field-induced metallization of such materials from their insulating states could enable a new class of ultrafast electronic switches and latches. However, significant questions remain about the detailed nature of the switching process.

Suppression of ionic liquid gate-induced metallization of SrTiO3(001) by oxygen.

Ionic liquid gating of three terminal field effect transistor devices with channels formed from SrTiO3(001) single crystals induces a metallic state in the channel. We show that the metallization is strongly affected by the presence of oxygen gas introduced external to the device whereas argon and nitrogen have no effect. The suppression of the gating effect is consistent with electric field induced migration of oxygen that we model by oxygen-induced carrier annihilation.

Crystal-facet-dependent metallization in electrolyte-gated rutile TiO2 single crystals.

The electric-field-induced metallization of insulating oxides is a powerful means of exploring and creating exotic electronic states. Here we show by the use of ionic liquid gating that two distinct facets of rutile TiO2, namely, (101) and (001), show clear evidence of metallization, with a disorder-induced metal-insulator transition at low temperatures, whereas two other facets, (110) and (100), show no substantial effects. This facet-dependent metallization can be correlated with the surface energy of the respective crystal facet and, thus, is consistent with oxygen vacancy formation and diffusion that results from the electric fields generated within the electric double layers at the ionic liquid/TiO2 interface.

Suppression of metal-insulator transition in VO2 by electric field-induced oxygen vacancy formation.

Electrolyte gating with ionic liquids is a powerful tool for inducing novel conducting phases in correlated insulators. An archetypal correlated material is vanadium dioxide (VO(2)), which is insulating only at temperatures below a characteristic phase transition temperature. We show that electrolyte gating of epitaxial thin films of VO(2) suppresses the metal-to-insulator transition and stabilizes the metallic phase to temperatures below 5 kelvin, even after the ionic liquid is completely removed.

Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers.

Magnetically engineered magnetic tunnel junctions (MTJs) show promise as non-volatile storage cells in high-performance solid-state magnetic random access memories (MRAM). The performance of these devices is currently limited by the modest (< approximately 70%) room-temperature tunnelling magnetoresistance (TMR) of technologically relevant MTJs. Much higher TMR values have been theoretically predicted for perfectly ordered (100) oriented single-crystalline Fe/MgO/Fe MTJs.