Magnetization switching by the interaction between spins and charges has greatly brightened the future of spintronic memories. [1][2][3][4][5][6] This has been evident in the rapid development of spin transfer torque-magnetic random-access memory (STT-MRAM) as a mainstream non-volatile memory technology, in which a spin-polarized current is injected into magnetic tunnel junctions (MTJs) for cell programming. 7-18 However, as cell areas scale down to meet density and power demands, conventional STT-MRAM suffers from serious endurance and reliability issues due to the aging of the ultrathin MgO barrier and read disturbance. The challenge of lowering STT switching current densities to further reduce power consumption is still yet to be met. [19][20][21] The discovery of spin-orbit torque (SOT) switching in heavy metal/ferromagnetic metal/oxide heterostructures by applying an in-plane charge current to three-terminal devices provides a promising alternative mechanism. 22-28 It shows the potential to enhance the endurance and reliability of MRAM, while improving speed and reducing power consumption. [29][30][31][32] Thus, considerable research has been triggered to further elucidate the mechanism of SOT switching, which is currently described as magnetic reversal via two vector components, the damping-like (DL) and field-like (FL) torques. 33,34 Since the demonstration of perpendicular-anisotropy MgO/CoFeB MTJs (p-MTJs), the switching of perpendicular magnetization by SOT has become of particular interest. [33][34][35][36][37][38] However, an external magnetic field collinear with the charge current is required to execute deterministic switching of p-MTJs. This intrinsic constraint, combined with the three-terminal device configuration, is limiting the practical application of SOT-MRAM. [26][27][28]35 Great efforts have been made to eliminate the need

The electrical manipulation of magnetization and exchange bias in antiferromagnet/ferromagnet thin films could be of use in the development of the next generation of spintronic devices. Currentcontrolled magnetization switching can be driven by spin-orbit torques generated in an adjacent heavy metal layer, but these structures are difficult to integrate with exchange bias switching and tunnelling magnetoresistance measurements. Here, we report the current-induced switching of exchange bias field in a perpendicularly magnetized IrMn/CoFeB bilayer structure using a spinorbit torque generated in the antiferromagnet IrMn layer. By manipulating the current direction and amplitude, independent and repeatable switching of the magnetization and exchange bias field below the blocking temperature can be achieved. The critical current density for the exchange bias switching is found to be larger than that for CoFeB magnetization reversal. X-ray magnetic circular dichroism, polarized neutron reflectometry measurements and micromagnetic simulations show that a small net magnetization within the IrMn interface plays a crucial role in these phenomena.2 Electrical manipulation of the magnetization and exchange bias in antiferromagnet (AFM)/ferromagnet (FM) heterostructures 1-10 is expected to be of use in several high-performance spintronic devices, including magnetic tunnel junctions and magnetoresistance sensors. An efficient method for electrical switching of the FM magnetization is to use the spin-orbit torque (SOT) generated from a heavy metal (such as W, Ta, Pt) layer in AFM/FM/heavy metal structures 4,5,[11][12][13][14] .The in-plane exchange field generated at the AFM/FM interface enables field-free switching of the perpendicular magnetization and, compared to spin-transfer torque (STT)-driven devices, SOTdriven systems can potentially offer decreased switching times and thus faster data writing 15 .However, manipulation of the exchange bias is usually achieved by field cooling, which requires an external magnetic field and high temperature, hindering its application in practical devices 1,16,17 .Alternatively, it has recently been demonstrated that the exchange bias field at the AFM/FM interface can be switched by the SOT generated in the Pt layer in a Pt/Co/IrMn structure, passing through the thin Co layer 6 . Strong SOTs can also be generated in certain AFM thin films (such as IrMn and PtMn) due to their giant spin Hall angle [18][19][20][21][22] , allowing simpler spintronic devices to be created [23][24][25] . For example, field-free switching of perpendicular magnetization has been achieved in PtMn/[Co/Ni]n structures where no heavy metal layer is required, with both the in-plane exchange bias and SOT originating from the AFM/FM system 23 . An advantage of using an AFM/FM/oxide stack is that it is easier, compared to AFM/FM/heavy metal structures, to integrate tunnelling magnetoresistance (for electrical reading of FM magnetization 26,27 ), SOT and exchange bias switching in a single device.In this Article, we repo...

Neuromorphic computing, which relies on a combination of a large number of neurons massively interconnected by an even larger number of synapses, has been actively studied for its characteristics such as energy efficiency, intelligence, and adaptability. To date, while the development of artificial synapses has shown great progress with the introduction of emerging nanoelectronic devices, e.g., memristive devices, the implementation of artificial neurons, however, depends mostly on semiconductor-based circuits via integrating many transistors, sacrificing energy efficiency and integration density. Here, we present a novel compact neuron device that exploits the current-driven magnetic skyrmion dynamics in a wedge-shaped nanotrack. Under the coaction of the exciting current pulse and the repulsive force exerted by the nanotrack edges, the dynamic behavior of the proposed skyrmionic artificial neuron device is in analogy to the leaky-integrate-fire (LIF) spiking function of a biological neuron. The tunable temporary location of the skyrmion in our artificial neuron behaves like the analog membrane potential of a biological neuron. The neuronal dynamics and the related physical interpretations of the proposed skyrmionic neuron device are carefully investigated via micromagnetic and theoretical methods. Such a compact artificial neuron enables energy-efficient and high-density implementation of neuromorphic computing hardware.

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