Switching Of Magnetic Moments Research Articles

Магнитоэлектроакустическая динамика в стрейнтронной ячейке памяти с произвольным доступом

Straintronic principle of nonvolatile magnetoelectric random access memory (MELRAM) draws much attention due to the prospects of ultra-low energy consumption in storage devices. The switching of magnetic moments by pulsed deformation of elastically coupled magnetic and piezoelectric subsystems is accompanied by excitation of acoustic oscillations in the memory cells. Oscillation period in nanoscale cells is comparable with the magnetic moment switching time, which can affect the information recording process. In the present paper the influence of acoustic excitations on the magnetic switching dynamics is studied by numerical modeling with application to a magnetostrictive cell 50×50×400 nm3 on a PMN-PT <011> substrate. Parameters of voltage control pulses that can insure reliable switching of magnetic states of the system are determined.

LAS-NCS: A Laser-Assisted Spintronic Neuromorphic Computing System

In spintronic-based neuromorphic computing systems (NCSs), the switching of magnetic moment in a magnetic tunnel junction (MTJ) is used to mimic biological neuron firing. However, the high currents required for MTJ switching will lead to a large energy consumption and low speed operation of the MTJ-based NCSs. In this brief, the energy consumption and the delay of the proposed MTJ-based NCS are reduced by thermally assisting the MTJ switching through a microwatt nanosecond laser pulse. Simulation results show 85.7%, 84%, and 97.8% improvements in energy consumption, delay, and energy-delay product, respectively, for the laser-assisted spintronic NCS (LAS-NCS) by heating the MTJs up to 127 °C. The energy consumption of the laser pulse for heating up the MTJ stack is $1.2 {\times }$ – $2.4 {\times }$ lower than Joule heating method. Moreover, in contrast with Joule heating method, the LAS-NCS does not require MTJ with modified structure.

A Low-Power High-Speed Spintronics-Based Neuromorphic Computing System Using Real-Time Tracking Method

In spintronic-based neuromorphic computing systems (NCSs), the switching of magnetic moment in a magnetic tunnel junction (MTJ) is used to mimic neuron firing. However, the stochastic switching behavior of the MTJ and process variations effect lead to a significant increase in the stimulation time of such NCSs. Moreover, current NCSs need an extra phase to read the MTJ state after stimulation, which is in contrast with real neuron functionality in human body. In this paper, the read circuit is replaced with a proposed real-time sensing (RTS) circuit. The RTS circuit tracks the MTJ state during stimulation phase. As soon as switching happens, the RTS circuit terminates the MTJ current and stimulates the post neuron. Hence, the RTS circuit not only improves the energy consumption and speed, but also makes the operation of the NCS similar to real neuron functionality. The simulation results in 65-nm CMOS technology confirm that the energy consumption and speed of the proposed RTS-based NCS are improved at least by 40% and 2.22X compared with a typical NCS, respectively. Finally, utilizing the RTS-based NCS in image processing applications, such as character recognition and edge detection, can lead to 90.3% improvement in energy delay products compared with the typical NCS.

Simulating Study on Microwave Assisted Switching of Ferromagnetic Moment for Grains

The minimum switching field threshold and switching speed are important parameters for the magnetic recording in writing. This paper presents the dynamic precession of the moments of the grains based on LL equation, and that the impact of the volume of the grain on the switching speed is investigated under the condition of microwave assisted switching of magnetic moment.

Pinning and switching of magnetic moments in bilayer graphene

We examine the magnetic properties of the localized states induced by lattice vacancies in bilayer graphene with an unrestricted Hartree–Fock calculation. We show that, with realistic values of the parameters and for experimentally accessible gate voltages, we can have magnetic switching between an unpolarized and a fully polarized system.

Tunneling magnetoresistance in small dot arrays with perpendicular anisotropy

The tunneling magnetoresistance (TMR) of a small magnetic dot array with perpendicular anisotropy, is studied by using a resistor network model. Because of the competition between dipolar interaction and perpendicular anisotropy, the TMR ratio can be up to a maximum value (~26%) as predicted by a theoretical model. At moderate dipolar interaction strength, the perpendicular TMR ratio exhibits abrupt jumps due to the switching of magnetic moments in the array when the applied field (normal to the array plane) decreases from a saturation field. This novel character does not occur if the dipolar interaction between particles is quite strong. Furthermore, the effect of the array size N on TMR is also studied and the result shows that TMR ratio fluctuates when N increases for a moderate dipolar interaction strength. When the applied field he is parallel to the array plane, the in-plane TMR curve seems insensitive to the dipolar interaction strength, but the maximum TMR ratio (~26%) can also be obtained at he=0.

Magnetic property enhancement of Fe/sub 49-x/Co/sub x/Pt/sub 51/ (x=0.0,0.7,1.3,2.2) thin films

Magnetic properties of Fe/sub 49-x/Co/sub x/Pt/sub 51/ (x=0.0,0.7,1.3, and 2.2) thin films are investigated. Cobalt is found to enhance the magnetization and energy product of the films. A maximum energy product of 18.4 MGOe is obtained at x=1.3. This value is 87% larger than that of a binary FePt film. High-saturation magnetization of M/sub s/=1180 emu/cm/sup 3/ and remanent magnetization of M/sub r/=862emu/cm/sup 3/ are obtained as the sample with x=1.3 was annealed at 500/spl deg/C. The addition of cobalt increases the ordering temperature of the film, which retains more disordered phase in the film and thus produces higher magnetization than the binary sample. Exchange coupling is found to exist between ordered and disordered FePt phases. The intensive intergranular exchange coupling also makes the switching of magnetic moments in the thin film more cooperative. We consider that both the magnetization enhancement and the cooperated switching behavior in the thin film are responsible for the increased energy product.