Fast Memory Devices Research Articles

Josephson current-assisted reversal of a single-domain nanoscale ferromagnet driven by cosine chirp pulse

We study the microwave-induced magnetization reversal in two systems, the microwave-driven nanomagnet (NM) and the NM coupled to a Josephson junction (JJ) under the microwave field (NM-JJ-MW). The frequency of the applied cosine chirp pulse changes nonlinearly with time to match the magnetization precession frequency. The coupling between the NM and JJ reduces the magnetization switching time as well as the optimal amplitude of the microwave field as a result of manipulating the magnetization via Josephson-to-magnetic energy ratio G. The reversal effect in NM-JJ-MW is sufficiently robust against changes in pulse amplitude and duration. In this system, the increase of G decreases the possibility of the non-reversing magnetic response as the Gilbert damping increases without further increase in the external microwave field. We also discuss the magnetic response of the NM driven by the ac field of two JJs in which the time-dependent frequency is controlled by the voltage across the junctions. Our results provide a controllable scheme of magnetization reversal that might help to realize fast memory devices.

Atomistic Modeling of Spin and Electron Dynamics in Two-Dimensional Magnets Switched by Two-Dimensional Topological Insulators

To design fast memory devices, we need material combinations that can facilitate fast read and write operations. We present a heterostructure comprising a two-dimensional (2D) magnet and a 2D topological insulator (TI) as a viable option for designing fast memory devices. We theoretically model the spin-charge dynamics between 2D magnets and 2D TIs. Using the adiabatic approximation, we combine the nonequilibrium Green's function method for spin-dependent electron transport and a time-quantified Monte Carlo method for simulating magnetization dynamics. We show that it is possible to switch a magnetic domain of a ferromagnet using the spin torque from spin-polarized edge states of a 2D TI. We show further that the switching of 2D magnets by TIs is strongly dependent on the interface exchange (${J}_{\mathrm{int}}$), and an optimal interface exchange, is required for efficient switching. Finally, we compare experimentally grown Cr compounds and show that Cr compounds with higher anisotropy (such as $\mathrm{Cr}{\mathrm{I}}_{3}$) result in a lower switching speed but a more stable magnetic order.

A change in computing [skyrmions

The chances are high that most people you know have never heard of skyrmions. This is natural, because they are rather murky products of quantum field theory that act like particles without actually being particles. So far so obscure. Skyrmions, however, may soon be as well known as silicon chips. That's because they have the potential to change the face of computing, revolutionising the fields of data storage, information processing and artificial intelligence. Skyrmions are quasi-particles - little twists in energy fields that look and behave like particles. They can be moved around, interact with other skyrmions and be created and destroyed. Like particles, they can be extremely stable, lasting years in the right conditions. Based on their inherent stability, the most promising application for skyrmions is in data storage, where each skyrmion acts as a bit. However, there are challenges to overcome - researchers have only been able to find magnetic skyrmions that are too slow and too large to compete with existing memory devices. Until now. In December 2018, a team from MIT published a paper showing that they could achieve the right sizes and, to some degree, speeds to be competitive.The size, speed and stability of skyrmions could mean smaller and faster memory devices are around the corner. What's more, because of skyrmions' inherent stability, they are still there when you turn the power off. This means that something called normally-off computing could be achieved. Skyrmions' potential extends even beyond classical computing. Neuromorphic computing seeks to use neural networks to mimic the way the brain processes information and is behind some of the most powerful machine-learning algorithms.structure.

Resistive switching device based on high-mobility graphene and its switching mechanism

Graphene is a promising material for fast memory device, due to its high mobility and potential for ultrasmall linewidth. However, the high mobility are normally obtained with strict limitations, such as Boron nitride substrate and capping layer, or low temperature with mechanical exfoliation. In this paper, we modified the fabrication process of graphene device, and high carrier mobility larger than 10,000 cm2/(Vs) was obtained for graphene grown by chemical vapor deposition. Resistive switching devices based on these high mobility graphene were fabricated, and the conducting mechanism of the switching process were discussed in detail. A model based on a Schottky diode in series connection with a tunneling junction is found to be consistent with the conducting mechanism. Our results are useful for normal research groups with only traditional nanofabrication facility.

Quick Changes in Magnetic Materials

A class of magnetic materials can be reordered at the nanoscale more rapidly than the type usually found in magnetic hard drives, offering a possible route to faster memory devices.

Optical memory based on the long-term photon echo phenomenon

The possibility of using the long-term photon echo phenomenon as a basis for an optical memory device is considered. It is shown that all functions of a fast memory device can be achieved. Particularly, it is shown that multiple read-out and selective erasing of information in each cell are possible without influence on the information in other cells of the memory device.

An MC68030/MC68EC030 32 bit high performance system

The design of a 32 bit high performance system based on Motorola's MC68030/ MC68EC030 microprocessors is described. It makes use of the fast synchronous interface to access RAM memory with a two clock cycle read and write bus cycle. The system is designed to operate at 20 MHz using available fast static RAM memories, with future upgrades to 25 MHz and 33 MHz using faster memory devices.

Effects of hyperfine structures on an optical stimulated echo memory device

An optical three-pulse stimulated echo signal is analyzed theoretically and numerically for three pulses of arbitrary shape in a medium having hyperfine structures in the ground and excited states. The feasibility of its use as an optical fast-memory device is emphasized. Numerical analysis shows that the fidelity of the memory is reasonably good as long as the storage time T is short compared with the excited-state lifetime T1. However, the echo suffers severe modulation because of the hyperfine structures when T exceeds T1.