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. Here we show that sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented (100) MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to approximately 220% at room temperature and approximately 300% at low temperatures. Consistent with these high TMR values, superconducting tunnelling spectroscopy experiments indicate that the tunnelling current has a very high spin polarization of approximately 85%, which rivals that previously observed only using half-metallic ferromagnets. Such high values of spin polarization and TMR in readily manufactureable and highly thermally stable devices (up to 400 degrees C) will accelerate the development of new families of spintronic devices.

The origin of spin–orbit torques, which are generated by the conversion of charge-to-spin currents in non-magnetic materials, is of considerable debate. One of the most interesting materials is tungsten, for which large spin–orbit torques have been found in thin films that are stabilized in the A15 (β-phase) structure. Here we report large spin Hall angles of up to approximately –0.5 by incorporating oxygen into tungsten. While the incorporation of oxygen into the tungsten films leads to significant changes in their microstructure and electrical resistivity, the large spin Hall angles measured are found to be remarkably insensitive to the oxygen-doping level (12–44%). The invariance of the spin Hall angle for higher oxygen concentrations with the bulk properties of the films suggests that the spin–orbit torques in this system may originate dominantly from the interface rather than from the interior of the films.

A domain wall (DW) in a ferromagnetic nanowire (NW) is composed of elementary topological bulk and edge defects with integer and fractional winding numbers, respectively; whose relative spatial arrangement determines the chirality of the DW. Here we show how we can understand and control the trajectory of DWs in magnetic branched networks, composed of connected NWs, by a consideration of their fractional elementary topological defects and how they interact with those innate to the network. We first develop a highly reliable mechanism for the injection of a DW of a given chirality into a NW and show that its chirality determines which branch the DW follows at a symmetric Y--shaped magnetic junction --the fundamental

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. Here, we show, in the canonical metal-to-insulator transition system V₂O₃, that ultrafast voltage pulses result in its metallization only after an incubation time that ranges from ∼150 ps to many nanoseconds, depending on the electric field strength. We show that these incubation times can be accounted for by purely thermal effects and that intrinsic electronic-switching mechanisms may only be revealed using larger electric fields at even shorter timescales.

Spin-polarized charge currents induce magnetic tunnel junction (MTJ) switching by virtue of spin-transfer torque (STT). Recently, by taking advantage of the spin-dependent thermoelectric properties of magnetic materials, novel means of generating spin currents from temperature gradients, and their associated thermal-spin torques (TSTs), have been proposed, but so far these TSTs have not been large enough to influence MTJ switching. Here we demonstrate significant TSTs in MTJs by generating large temperature gradients across ultrathin MgO tunnel barriers that considerably affect the switching fields of the MTJ. We attribute the origin of the TST to an asymmetry of the tunneling conductance across the zero-bias voltage of the MTJ. Remarkably, we estimate through magneto-Seebeck voltage measurements that the charge currents that would be generated due to the temperature gradient would give rise to STT that is a thousand times too small to account for the changes in switching fields that we observe.MRAM | spintronics | spin caloritronics U sing heat to create potential gradients and charge currents has been a very active area of research in thermoelectrics (1). Spin caloritronics (2, 3) adds a new dimension to this concept by considering the use of heat to create spin-dependent chemical potential gradients in ferromagnetic materials (4). Traditionally, electric-current-driven spin currents have been used to transport spin angular momentum to change the magnetization of a magnetic material--a phenomenon known as spin-transfer torque (STT) (5-7). Heat currents can also create spin currents in magnetic materials; the transfer of spin angular momentum through this process has been named thermal-spin torque (TST) (8,9). A panoply of recent experiments that use spin currents generated by heat has been reported which includes the spin-Seebeck effect observed in ferromagnetic metals (10, 11), semiconductors (12) and insulators (13), thermal-spin injection from a ferromagnet into a nonmagnetic metal (14), the magnetoSeebeck effect observed in magnetic tunnel junctions (MTJ) (15-17), Seebeck spin tunneling in ferromagnet-oxide-silicon tunnel junctions (18), and several others (19,20). On the other hand, whereas there have been several theoretical predictions (8,9,21,22) of the TST, there have been few experiments to date. In one experiment, evidence of TST was established in Co-Cu-Co spinvalve nanowires (23). However, in this work the same current was used for both heating and probing the device, thus making it difficult to unravel the individual contribution of TST from the simultaneously generated STT.In our device, the heating current is distinct from the probing current, which helps to decouple pure temperature gradient effects from charge-current-driven STT effects. We find that a temperature gradient of ∼1 K/nm across a 0.9-nm-thick MgO tunnel barrier in an MTJ induces modest charge currents on the order of 1 × 10 3

We demonstrate a highly efficient and simple scheme for injecting domain walls into magnetic nanowires. The spin transfer torque from nanosecond long, unipolar, current pulses that cross a 90° magnetization boundary together with the fringing magnetic fields inherently prevalent at the boundary, allow for the injection of single or a continual stream of domain walls. Remarkably, the currents needed for this "in-line" domain wall injection scheme are at least one hundred times smaller than conventional methods.

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Recent developments in spin-orbit torques allow for highly efficient current-driven domain wall (DW) motion in nanowires with perpendicular magnetic anisotropy. Here, we show that chiral DWs can be driven into nonequilibrium states that can persist over tens of nanoseconds in Y-shaped magnetic nanowire junctions that have an input and two symmetric outputs. A single DW that is injected into the input splits and travels at very different velocities in the two output branches until it reaches its steady-state velocity. We find that this is due to the disparity between the fast temporal evolution of the spin current derived spin-orbit torque and a much-slower temporal evolution of the DMI-derived torque. Changing the DW polarity inverts the velocity asymmetry in the two output branches, a property that we use to demonstrate the sorting of domains.