In most ferromagnets the magnetization rotates from one domain to the next with no preferred handedness. However, broken inversion symmetry can lift the chiral degeneracy, leading to topologically-rich spin textures such as spin-spirals 1,2 and skyrmions 3-5 via the Dzyaloshinskii-Moriya interaction (DMI)6 . Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy metal and an oxide, the DMI stabilizes chiral domain walls (DWs) 2,7 whose spin texture enables extremely efficient current-driven motion [8][9][10][11] . We show that spin torque from the spin Hall effect [12][13][14][15] The Rashba field lacks the correct symmetry to drive DWs directly 16,26,27 , and the spin Hall effect (SHE) in the adjacent heavy metal has emerged as a possible alternative mechanism [12][13][14][15][16]27 . SHE-driven spin accumulation at the heavy-metal/ferromagnet interface generates a Slonczeswki-like torque 16,26,27 strong enough to switch uniformly-magnetized films [12][13][14][15]18 . However, the Bloch DWs expected in typical nanowire geometries [8][9][10][11]28 have their plane oriented perpendicular to the nanowire axis, in which case the Slonczewski-like torque vanishes 16 . This behavior was recently confirmed in asymmetric Pt/Co/Pt stacks in which the SHE-induced torques from the Pt layers did not cancel completely 15 . In that case, currentassisted DW depinning was observed when an applied field rotated the DW plane towards the current axis, but up-down and down-up DWs were driven in opposite directions and the current had no effect in the absence of the bias field. The SHE alone is therefore incapable of uniformly 3 driving trains of DWs in devices, and is insufficient to explain the high spin-torque efficiencies and DW velocities observed in Pt/Co/oxide 8-11 without applied fields.Here we characterize current-induced torques and DW dynamics in out-of-plane magnetized Pt/CoFe/MgO and Ta/CoFe/MgO stacks that are nominally identical except for the heavy-metal underlayers, whose spin Hall angles are large and of opposite sign [12][13][14] . By considering the symmetry of the measured current-induced torque along with the DW dynamics driven by this torque, we uniquely identify the DW configuration as Néel with a fixed chirality.Magnetostatics alone makes this configuration unstable and does not favor one chirality over the other, but the DMI has been theoretically shown to promote chiral Néel DWs 2,7 . By applying inplane magnetic fields, we verify that the DW magnetization aligns rigidly along the nanowire axis, and that the DW spin spiral exhibits a global chirality common to both Pt/CoFe/MgO and Ta/CoFe/MgO. Current-driven DW motion in heavy-metal/ferromagnet/oxide structures is naturally explained by the combination of the SHE, which produces the sole current-induced torque, and the DMI, which stabilizes chiral DWs whose symmetry permits uniform motion with very high efficiency.DW motion was characterized in 500-nm wide, 40-μm long nanowires overlaid with an orthogonal DW nucleation li...

Magnetic skyrmions are topologically protected spin textures that exhibit fascinating physical behaviours and large potential in highly energy-efficient spintronic device applications. The main obstacles so far are that skyrmions have been observed in only a few exotic materials and at low temperatures, and fast current-driven motion of individual skyrmions has not yet been achieved. Here, we report the observation of stable magnetic skyrmions at room temperature in ultrathin transition metal ferromagnets with magnetic transmission soft X-ray microscopy. We demonstrate the ability to generate stable skyrmion lattices and drive trains of individual skyrmions by short current pulses along a magnetic racetrack at speeds exceeding 100 m s(-1) as required for applications. Our findings provide experimental evidence of recent predictions and open the door to room-temperature skyrmion spintronics in robust thin-film heterostructures.

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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 magneto-electric coupling mechanisms. We directly observe in situ voltage-driven O(2-) migration in a Co/metal-oxide bilayer, which we use to toggle the interfacial magnetic anisotropy energy by >0.75 erg cm(-2) at just 2 V. We exploit the thermally activated nature of ion migration to markedly 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.

This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.

Ferromagnetic nanowires are likely to play an important role in future spintronic devices. Magnetic domain walls, which separate regions of opposing magnetization in a nanowire, can be manipulated and used to encode information for storage or to perform logic operations. Owing to their reduced size and dimensionality, the characterization of domain-wall motion is an important problem. To compete with other technologies, high-speed operation, and hence fast wall propagation, is essential. However, the domain-wall dynamics in nanowires has only been investigated in the last five years and some results indicate a drastic slowing down of wall motion in higher magnetic fields. Here we show that the velocity-field characteristic of a domain wall in a nanowire shows two linear regimes, with the wall mobility at high fields reduced tenfold from that at low fields. The transition is marked by a region of negative differential mobility and highly irregular wall motion. These results are in accord with theoretical predictions that, above a threshold field, uniform wall movement gives way to turbulent wall motion, leading to a substantial drop in wall mobility. Our results help resolve contradictory reports of wall propagation velocities in laterally confined geometries, and underscore the importance of understanding and enhancing the breakdown field for practical applications.

Spintronics is a research field that aims to understand and control spins on the nanoscale and should enable next-generation data storage and manipulation. One technological and scientific key challenge is to stabilize small spin textures and to move them efficiently with high velocities. For a long time, research focused on ferromagnetic materials, but ferromagnets show fundamental limits for speed and size. Here, we circumvent these limits using compensated ferrimagnets. Using ferrimagnetic Pt/GdCo/TaO films with a sizeable Dzyaloshinskii-Moriya interaction, we realize a current-driven domain wall motion with a speed of 1.3 km s near the angular momentum compensation temperature (T) and room-temperature-stable skyrmions with minimum diameters close to 10 nm near the magnetic compensation temperature (T). Both the size and dynamics of the ferrimagnet are in excellent agreement with a simplified effective ferromagnet theory. Our work shows that high-speed, high-density spintronics devices based on current-driven spin textures can be realized using materials in which T and T are close together.

Magnetic skyrmions are topological quasiparticles of great interest for data storage applications because of their small size, high stability, and ease of manipulation via electric current. However, although models exist for some limiting cases, there is no universal theory capable of accurately describing the structure and energetics of all skyrmions. The main barrier is the complexity of non-local stray field interactions, which are usually included through crude approximations. Here we present an accurate analytical framework to treat isolated skyrmions in any material, assuming only a circularly-symmetric 360° domain wall profile and a homogeneous magnetization profile in the out-of-plane direction. We establish the first rigorous criteria to distinguish stray field from DMI skyrmions, resolving a major dispute in the community. We discover new phases, such as bi-stability, a phenomenon unknown in magnetism so far. We predict materials for sub-10 nm zero field room temperature stable skyrmions suitable for applications. Finally, we derive analytical equations to describe current-driven dynamics, find a topological damping, and show how to engineer materials in which compact skyrmions can be driven at velocities >1000 m/s.