Magnetic oxides exhibit rich fundamental physics1–4 and technologically desirable properties for spin-based memory, logic and signal transmission5–7. Recently, spin–orbit-induced spin transport phenomena have been realized in insulating magnetic oxides by using proximate heavy metal layers such as platinum8–10. In their metallic ferromagnet counterparts, such interfaces also give rise to a Dzyaloshinskii–Moriya interaction11–13 that can stabilize homochiral domain walls and skyrmions with efficient current-driven dynamics. However, chiral magnetism in centrosymmetric oxides has not yet been observed. Here we discover chiral magnetism that allows for pure spin-current-driven domain wall motion in the most ubiquitous class of magnetic oxides, ferrimagnetic iron garnets. We show that epitaxial rare-earth iron garnet films with perpendicular magnetic anisotropy exhibit homochiral Néel domain walls that can be propelled faster than 800 m s−1 by spin current from an adjacent platinum layer. We find that, despite the relatively small interfacial Dzyaloshinskii–Moriya interaction, very high velocities can be attained due to the antiferromagnetic spin dynamics associated with ferrimagnetic order. Spin currents from an adjacent Pt layer can drive homochiral Néel domain walls in centrosymmetric rare-earth iron garnet films at more than 800 m s–1, taking advantage of the antiferromagnetic spin dynamics of the ferrimagnetic oxide.

Magnetic skyrmions promise breakthroughs in future memory and computing devices due to their inherent stability and small size. Their creation and current driven motion have been recently observed at room temperature, but the key mechanisms of their formation are not yet well-understood. Here it is shown that in heavy metal/ferromagnet heterostructures, pulsed currents can drive morphological transitions between labyrinth-like, stripe-like, and skyrmionic states. Using high-resolution X-ray microscopy, the spin texture evolution with temperature and magnetic field is imaged and it is demonstrated that with transient Joule heating, topological charges can be injected into the system, driving it across the stripe-skyrmion boundary. The observations are explained through atomistic spin dynamic and micromagnetic simulations that reveal a crossover to a global skyrmionic ground state above a threshold magnetic field, which is found to decrease with increasing temperature. It is demonstrated how by tuning the phase stability, one can reliably generate skyrmions by short current pulses and stabilize them at zero field, providing new means to create and manipulate spin textures in engineered chiral ferromagnets.

Magnetic skyrmions are particle-like chiral twists of the magnetization that promise advances in spin-based data storage and logic device applications. In article number 1805461, Mathias Kläui, Geoffrey S. D. Beach, and co-workers examine current-induced generation of skyrmions in heavy-metal/ferromagnet multilayers and show that Joule heat pulses can drive topological transitions in magnetic textures and enable skyrmion creation on nanosecond timescales.

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/Gd44Co56/TaOx films with a sizeable Dzyaloshinskii–Moriya interaction, we realize a current-driven domain wall motion with a speed of 1.3 km s–1 near the angular momentum compensation temperature (TA) and room-temperature-stable skyrmions with minimum diameters close to 10 nm near the magnetic compensation temperature (TM). 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 TA and TM are close together. Ferrimagnetic Gd44Co56 near the compensation temperature enables domain wall motion with a speed of 1.3 km s–1 and room temperature skyrmions with diameters close to 10 nm.

Voltage-gated ion transport as a means of manipulating magnetism electrically could enable ultralow-power memory, logic and sensor technologies. Earlier work made use of electric-field-driven O2- displacement to modulate magnetism in thin films by controlling interfacial or bulk oxidation states. However, elevated temperatures are required and chemical and structural changes lead to irreversibility and device degradation. Here we show reversible and non-destructive toggling of magnetic anisotropy at room temperature using a small gate voltage through H+ pumping in all-solid-state heterostructures. We achieve 90° magnetization switching by H+ insertion at a Co/GdOx interface, with no degradation in magnetic properties after >2,000 cycles. We then demonstrate reversible anisotropy gating by hydrogen loading in Pd/Co/Pd heterostructures, making metal-metal interfaces susceptible to voltage control. The hydrogen storage metals Pd and Pt are high spin-orbit coupling materials commonly used to generate perpendicular magnetic anisotropy, Dzyaloshinskii-Moriya interaction, and spin-orbit torques in ferromagnet/heavy-metal heterostructures. Thus, our work provides a platform for voltage-controlled spin-orbitronics.

Magnetic insulators (MIs), especially iron-based garnets, possess remarkable properties such as ultralow damping and long magnon decay lengths, which can provide significant advantages for practical applications with respect to their metallic magnetic counterparts. Recently, robust perpendicular magnetic anisotropy (PMA) is obtained in ferrimagnetic films of thulium, europium, and terbium iron garnet (TmIG, EuIG, and TbIG) with high structural quality down to a thickness of 5.6 nm with saturation magnetization close to bulk [1,2]. By using the spin Hall effect in platinum we have demonstrated efficient spin current injection through the TmIG/Pt interface, which we quantified by the spin Hall magnetoresistance and harmonic Hall effect measurements [1-3]. We then achieved deterministic spin-orbit torque-driven magnetization switching of TmIG(~10 nm)/Pt bilayer both with quasi-dc (5 ms) as well as pulsed currents down to 2 ns width[1,4]. The switching current density is found to be of the order of ~10^7 (~10^8) A/cm2 using dc (pulsed) current, comparable to reported values for Pt/Co[5]. We reveal that the threshold switching current strongly depends on the absence or presence of an initially reversed domain in the structure implying a reversal mediated by efficient current-driven domain wall motion. Ultimately, we investigated the current-driven dynamics of domain walls in TmIG. We found that by solely using electrical currents, domain walls can be efficiently moved with very high mobility. Moreover, the flow regime threshold is found to be an order of magnitude lower with respect to conventional ferromagnets with interfacial PMA, owing to structural quality and bulk-like behavior of 7-nm-thick TmIG. These results suggest the utility of PMA rare earth garnets and pave the road towards ultralow dissipation spintronic devices based on MIs. [1] Avci et al., Nat. Mater. 16, 309 (2017); [2]Quindeau et al., Adv. Elec. Mater. 3, 1600376 (2017); [3]Avci et al., PRB 95, 115428 (2017); [4]Avci et al., APL 111, 072406 (2017); [5]Miron et al., Nature 476, 189 (2011).

With recent developments in the field of spintronics, ferromagnetic insulator (FMI) thin films have emerged as an important component of spintronic devices. Ferrimagnetic yttrium iron garnet in particular is an excellent insulator with low Gilbert damping and a Curie temperature well above room temperature, and has been incorporated into heterostructures that exhibit a plethora of spintronic phenomena including spin pumping, spin Seebeck, and proximity effects. However, it has been a challenge to develop high quality sub-10 nm thickness FMI garnet films with perpendicular magnetic anisotropy (PMA) and PMA garnet/heavy metal heterostructures to facilitate advances in spin-current and anomalous Hall phenomena. Here, robust PMA in ultrathin thulium iron garnet (TmIG) films of high structural quality down to a thickness of 5.6 nm are demonstrated, which retain a saturation magnetization close to bulk. It is shown that TmIG/Pt bilayers exhibit a large spin Hall magnetoresistance (SMR) and SMR-driven anomalous Hall effect, which indicates efficient spin transmission across the TmIG/Pt interface. These measurements are used to quantify the interfacial spin mixing conductance in TmIG/Pt and the temperature-dependent PMA of the TmIG thin film.

Spin-orbit torques and current-induced switching are studied in perpendicularly magnetized Pt/Au/(Co/Ni/Co) films as a function of Au insertion layer thickness tAu. By simultaneously varying the ferromagnet layer thickness, a parametric series of samples with nearly constant anisotropy were prepared. On this series, spin orbit torques were characterized by harmonic voltage and hysteresis loop shift measurements, and current-induced switching was examined as a function of the in-plane bias field. Little variation is seen for tAu < 0.5 nm, whereas for tAu > 0.5 nm, a series of well-correlated effects appear. Both the loop shift efficiency and the Slonczewski-like spin-orbit torque effective field double, while the in-plane field required to saturate the loop shift efficiency decreases by a factor of ∼10. Correspondingly, the current and in-plane field required for spin-orbit torque switching are reduced by about 90%. These results suggest that a thin Au insertion layer reduces the Dzyaloshinskii-Moriya interaction strength and improves spin transmission at the spin Hall metal/ferromagnet interface, substantially reducing the in-plane field and currents for spin orbit torque switching.

We characterize the spin Hall magnetoresistance (SMR), spin Seebeck effect (SSE), and dampinglike spin-orbit torque (SOT) in thulium iron garnet/platinum bilayers with perpendicular magnetic anisotropy by using harmonic Hall effect measurements. By consecutive annealing steps followed by measurements on a single device, we reveal that the spin-dependent effects gradually decrease in amplitude as the annealing temperature increases. We attribute this behavior primarily to the changes in the spin-mixing conductance, which sensitively depends on the interface quality. However, further analysis demonstrates that although the SSE scales closely with the SMR, the dampinglike SOT shows a significantly different trend upon annealing, contrary to theoretical expectations. By comparing the dampinglike SOT with the field-induced Hall effect, we found evidence that scattering from Fe impurities in the Pt at the interface might be responsible for the distinct annealing temperature dependence of the dampinglike SOT.

A solid-state three-terminal resistive switch based on gate-voltage-tunable reversible oxidation of a thin-film metallic channel is demonstrated. The switch is composed of a cobalt wire placed under a GdOx layer and a Au top electrode. The lateral resistance of the wire changes with the transition between cobalt and cobalt oxide controlled by a voltage applied to the top electrode. The kinetics of the oxidation and reduction process are examined through time-and temperature-dependent transport measurements. It is shown that that reversible voltage induced lateral resistance switching with a ratio of 103 can be achieved at room temperature. The reversible non-volatile redox reaction between metal and metal oxide may provide additional degrees of freedom for post-fabrication control of properties of solid-state materials. This type of three-terminal device has potential applications in neuromorphic computing and multilevel data storage, as well as applications that require controlling a relatively large current.

We report on a memory device concept based on the recently discovered unidirectional spin Hall magnetoresistance (USMR), which can store multiple bits of information in a single ferromagnetic heterostructure. We show that the USMR with possible contribution of Joule heating-driven magnetothermal effects in ferromagnet/normal metal/ferromagnet (FM/NM/FM) trilayers gives rise to four different 2nd harmonic resistance levels corresponding to four magnetization states (⇉, ⇄, ⇆, ⇇) in which the system can be found. Combined with the possibility of controlling the individual FMs by spin-orbit torques, we propose that it is possible to build an all-electrical lateral two-terminal multi-bit-per-cell memory device.

The temperature dependence of spin-orbit torques (SOTs) and spin-dependent transport parameters is measured in bilayer Ta/TbCo ferrimagnetic alloy films with bulk perpendicular magnetic anisotropy. We find that the dampinglike (DL)-SOT effective field diverges as temperature is swept through the magnetic compensation temperature (${T}_{\mathrm{M}}$), where the net magnetization vanishes due to the opposing contributions from the Tb and Co sublattices. We show that DL-SOT scales with the inverse of the saturation magnetization (${M}_{\mathrm{s}}$), whereas the spin-torque efficiency is independent of the temperature-dependent ${M}_{\mathrm{s}}$. Our findings provide insight into spin transport mechanisms in ferrimagnets and highlight low-${M}_{\mathrm{s}}$ rare-earth/transition-metal alloys as promising candidates for SOT device applications.

The magneto-ionic effect is a promising method to control the magnetic properties electrically. Charged mobile oxygen ions can easily be driven by an electric field to modify the magnetic anisotropy of a ferromagnetic layer in contact with an ionic conductor in a solid-state device. In this paper, we report on the room temperature magneto-ionic modulation of the magnetic anisotropy of ultrathin CoFeB films in contact with a GdOx layer, as probed by polar micro-Magneto Optical Kerr Effect during the application of a voltage across patterned capacitors. Both Pt/CoFeB/GdOx films with perpendicular magnetic anisotropy and Ta/CoFeB/GdOx films with uniaxial in-plane magnetic anisotropy in the as-grown state exhibit a sizable dependence of the magnetic anisotropy on the voltage (amplitude, polarity, and time) applied across the oxide. In Pt/CoFeB/GdOx multilayers, it is possible to reorient the magnetic anisotropy from perpendicular-to-plane to in-plane, with a variation of the magnetic anisotropy energy greater than 0.2 mJ m−2. As for Ta/CoFeB/GdOx multilayers, magneto-ionic effects still lead to a sizable variation of the in-plane magnetic anisotropy, but the anisotropy axis remains in-plane.