Spin-orbit Torque-driven Magnetization Switching Research Articles

Probability of spin-orbit torque driven magnetization switching assisted by spin-transfer torque

Probability of spin-orbit torque driven magnetization switching assisted by spin-transfer torque

Spin–orbit torque and Dzyaloshinskii–Moriya interaction in perpendicularly magnetized heterostructures with iridium

Spin–orbit torque and Dzyaloshinskii–Moriya interaction are systematically investigated in perpendicularly magnetized [Ni-Co]2/Ir heterostructures. From the thickness study, the spin Hall angle θSH and spin diffusion length lsd of Ir are determined to be θSH ≈ 0.005 and lsd ≈1.2 nm. Remarkably, it is found that by taking advantage of the low resistivity of Ir, the Ir-based device consumes less power for spin–orbit torque-driven magnetization switching compared to the one based on Pt or Ta. Furthermore, the Dzyaloshinskii–Moriya interaction field and coefficient D at the [Ni-Co]2/Ir interface are determined to be 174 Oe and 0.82 mJ m−2. This study suggests Ir as an advantageous material for ultralow-power and high-density spin–orbit torque memory and logic devices.

Field free magnetization switching in perpendicularly magnetized Pt/Co/FeNi/Ta structure by spin orbit torque

Spin orbit torque-driven magnetization switching in perpendicularly magnetized thin film relies on an extra in-plane magnetic field to break the in-plane magnetic symmetry, which is an obstacle for the integration of spin–orbit torque-based spintronic devices. Here, we propose a simple method to realize the field-free spin–orbit torque-driven magnetization switching by exploiting a tilted magnetic anisotropy, which is caused by the direct coupling of two ferromagnetic layers in the Pt/Co/FeNi/Ta structure. When preparing the sample, a 1000 Oe in-plane magnetic field was applied to ensure the magnetic moment deviating a small angle from the out-of-plane direction to this in-plane field direction. We experimentally demonstrate the deterministic field-free magnetization switching in Pt/Co/FeNi/Ta by the field-like spin–orbit torques when the electric current is applied perpendicular to this in-plane field direction. The switching performance is slightly degraded with the critical switching current density and thermal stability factor, respectively, reaching 6.4 × 106 A/cm2 and 25 due to the slightly decreased spin–orbit torque efficiency and perpendicular magnetic anisotropy with introducing the FeNi layers. Our work paves the way for realizing the field-free magnetization switching by spin–orbit torques.

Magnon-mediated spin currents in Tm3Fe5O12/Pt with perpendicular magnetic anisotropy

The control of pure spin currents carried by magnons in magnetic insulator (MI) garnet films with a robust perpendicular magnetic anisotropy (PMA) is of great interest to spintronic technology as they can be used to carry, transport, and process information. Garnet films with PMA have labyrinth domain magnetic structures that enrich the magnetization dynamics and could be employed in more efficient wave-based logic and memory computing devices. In MI/non-magnetic (NM) bilayers, where NM is a normal metal providing a strong spin–orbit coupling, the PMA benefits the spin–orbit torque-driven magnetization switching by lowering the needed current and rendering the process faster, crucial for developing magnetic random-access memories. In this work, we investigated the magnetic anisotropies in thulium iron garnet (TIG) films with PMA via ferromagnetic resonance measurements, followed by the excitation and detection of magnon-mediated pure spin currents in TIG/Pt driven by microwaves and heat currents. TIG films presented a Gilbert damping constant of α ≈0.01, with resonance fields above 3.5 kOe and half linewidths broader than 60 Oe, at 300 K and 9.5 GHz. The spin-to-charge current conversion through TIG/Pt was observed as a microvoltage generated at the edges of the Pt film. The obtained spin Seebeck coefficient was 0.54 μV/K, also confirming the high interfacial spin transparency.

Spin–orbit torque driven multi-level switching in He+ irradiated W–CoFeB–MgO Hall bars with perpendicular anisotropy

We have investigated the spin–orbit torque-driven magnetization switching in W/CoFeB/MgO Hall bars with perpendicular magnetic anisotropy. He+ ion irradiation through a mask has been used to reduce locally the effective perpendicular anisotropy at a Hall cross. Anomalous Hall effect measurements combined with Kerr microscopy indicate that the switching process is dominated by domain wall (DW) nucleation in the irradiated region followed by rapid domain propagation at a current density as low as 0.8 MA/cm2 with an assisting in-plane magnetic field. Thanks to the implemented strong pinning of the DW at the transition between the irradiated and the non-irradiated region, an intermediate Hall resistance state is induced, which is further verified by finite element simulations. Such a method to control electrically multi-level resistances using He+ ion irradiation shows great potential in realizing neuromorphic and memristor devices.

Room temperature magnetization switching in topological insulator-ferromagnet heterostructures by spin-orbit torques

Topological insulators with spin-momentum-locked topological surface states are expected to exhibit a giant spin-orbit torque in the topological insulator/ferromagnet systems. To date, the topological insulator spin-orbit torque-driven magnetization switching is solely reported in a Cr-doped topological insulator at 1.9 K. Here we directly show giant spin-orbit torque-driven magnetization switching in a Bi2Se3/NiFe heterostructure at room temperature captured using a magneto-optic Kerr effect microscope. We identify a large charge-to-spin conversion efficiency of ~1–1.75 in the thin Bi2Se3 films, where the topological surface states are dominant. In addition, we find the current density required for the magnetization switching is extremely low, ~6 × 105 A cm–2, which is one to two orders of magnitude smaller than that with heavy metals. Our demonstration of room temperature magnetization switching of a conventional 3d ferromagnet using Bi2Se3 may lead to potential innovations in topological insulator-based spintronic applications.

Spin-orbit torques in ferrimagnetic GdFeCo alloys

The spin-orbit torque switching of ferrimagnetic Gdx(Fe90Co10)100−x films was studied for both transition metal (TM)-rich and rare earth (RE)-rich configurations. The spin-orbit torque driven magnetization switching follows the same sense in TM-rich and RE-rich samples with respect to the total magnetization, but the sense of the switching is reversed with respect to the TM magnetization. This indicates that the sign of the spin-orbit-torque-driven magnetic switching follows the total magnetization, although transport based techniques such as anomalous Hall effect are only sensitive to the transition metal magnetization. These results provide important insight into the physics of spin angular momentum transfer in materials with antiferromagnetically coupled sublattices.

Spin orbit torques and Dzyaloshinskii-Moriya interaction in dual-interfaced Co-Ni multilayers

We study the spin orbit torque (SOT) and Dzyaloshinskii-Moriya interaction (DMI) in the dual-interfaced Co-Ni perpendicular multilayers. Through the combination of top and bottom layer materials (Pt, Ta, MgO and Cu), SOT and DMI are efficiently manipulated due to an enhancement or cancellation of the top and bottom contributions. However, SOT is found to originate mostly from the bulk of a heavy metal (HM), while DMI is more of interfacial origin. In addition, we find that the direction of the domain wall (DW) motion can be either along or against the electron flow depending on the DW tilting angle when there is a large DMI. Such an abnormal DW motion induces a large assist field required for hysteretic magnetization reversal. Our results provide insight into the role of DMI in SOT driven magnetization switching, and demonstrate the feasibility of achieving desirable SOT and DMI for spintronic devices.

Spin-orbit torque-driven magnetization switching and thermal effects studied in Ta\CoFeB\MgO nanowires

We demonstrate magnetization switching in out-of-plane magnetized Ta\CoFeB\MgO nanowires by current pulse injection along the nanowires, both with and without a constant and uniform magnetic field collinear to the current direction. We deduce that an effective torque arising from spin-orbit effects in the multilayer drives the switching mechanism. While the generation of a component of the magnetization along the current direction is crucial for the switching to occur, we observe that even without a longitudinal field thermally generated magnetization fluctuations can lead to switching. Analysis using a generalized Néel-Brown model enables key parameters of the thermally induced spin-orbit torques-driven switching process to be estimated, such as the attempt frequency and the effective energy barrier.