Depinning of domain walls in permalloy nanowires with asymmetric notches

Antiferromagnetic skyrmion-based high speed diode

Antiferromagnetic (AFM) skyrmions are favored over ferromagnetic (FM) skyrmions as they can be driven parallel to in-plane driving currents and eventually prevent the annihilation at the edges of nanotrack. In this study, an AFM skyrmion-based diode is proposed to realize the one-way skyrmion motion that is crucial for data processing in nanoelectronic and spintronic devices. The skyrmion transport is controlled by exploiting the staircase notch region in the middle of the nanotrack. By virtue of this, the micromagnetic interaction energy between the skyrmion and the notch edges generates a potential gradient that further gives rise to repulsive forces on the skyrmion. The resultant of the forces from the driving current and edge repulsions make the skyrmion move along the notch region to overcome the device window and reach the detection region. The notch is designed in such a way that it prevents the movement of the skyrmion in the reverse direction, thereby achieving diode functionality. The proposed device offers processing speed in the order of 10³ m s^-1, hence paving the way for the development of energy-efficient and high-speed devices in antiferromagnetic spintronics.

High-Resolution Scanning Electron Microscopy Imaging to Understand the Growth Kinetics of Nickel Nanorods

In the present work, the growth kinetics of nickel nanorods inside commercially available Whatman nanoporous membrane is explored to achieve uniform deposition over a large area of the membrane. Uniform electrodeposition inside nanopores requires continuous presence of solute ions near the deposition site and reduction of ions. To control ion diffusion and reduction near the deposition site, the effect of DC potential and pulsed potential with various duty cycles and solution temperatures is analyzed. Time-dependent variation in deposition current is recorded for all experiments. For different experimental conditions, high-resolution scanning electron microscopy (SEM) image is acquired. SEM along with the current density profile helped to understand the deposition mechanism for various growth conditions. Experiments confirmed that pulse deposition with a small duty cycle is promising to achieve uniform deposition. Also, by changing the pulse duty cycle, a sectioned nanostructure can be obtained. Based on the electron microscopic observation for various deposition conditions used in this work, it is concluded that initially nickel ions adhere to the pore surfaces due to high surface energy. When a potential is applied, ions reduce and a hollow nanotube structure forms. With time, concentric growth continues by forming a solid nanorod structure.

Voltage control of magnetic domain wall injection into strain-mediated multiferroic heterostructures

Effective control of domain wall (DW) injection into magnetic nanowires is of great importance for future novel device applications in spintronics, and currently relies on magnetization switching by the local external magnetic field obtained from metal contact lines or a spin-transfer torque (STT) effect from spin-polarized current. However, the external field is an obstacle for realizing practical spintronic devices with all-electric operation, and high current density can occasionally damage the devices. In this work, voltage controlled in-plane magnetic DW injection into a magnetic nanowire in the strain-mediated multiferroic heterostructures is studied by means of fully coupled micromagnetic-mechanical Finite Element Method (FEM) simulations. We propose an engineered shaped nano-magnet on a piezoelectric thin film in which a 180° magnetization rotation in the DW injection region is accomplished with in-plane piezostrain and magnetic shape anisotropy, thereby, leading to a DW injection into the nanowire. In this architecture, we computationally demonstrate repeated creation of DWs by voltage-induced strains without using any magnetic fields. Our FEM simulation results demonstrated an ultralow area energy consumption per injection (∼52.48 mJ m^-2), which is drastically lower than the traditional magnetic field and STT driven magnetization switching. A fast-overall injection time within ∼3.4 ns under continuous injection is also demonstrated. Further reduction of energy consumption and injection time can be achieved by optimization of the structure and material selections. The present design and computational analyses can provide an additional efficient method to realize low-power and high-speed spintronic and magnonic devices.

A Micromagnetic Protocol for Qualitatively Predicting Stochastic Domain Wall Pinning

Understanding dynamically-induced stochastic switching effects in soft ferromagnetic nanowires is a critical challenge for realising spintronic devices with deterministic switching behaviour. Here, we present a micromagnetic simulation protocol for qualitatively predicting dynamic stochastic domain wall (DW) pinning/depinning at artificial defect sites in Ni₈₀Fe₂₀ nanowires, and demonstrate its abilities by correlating its predictions with the results of focused magneto-optic Kerr effect measurements. We analyse DW pinning configurations in both thin nanowires (t = 10 nm) and thick nanowires (t = 40 nm) with both single (asymmetric) and double (symmetric) notches, showing how our approach provides understanding of the complex DW-defect interactions at the heart of stochastic pinning behaviours. Key results explained by our model include the total suppression of stochastic pinning at single notches in thick nanowires and the intrinsic stochasticity of pinning at double notches, despite their apparent insensitivity to DW chirality.