Mamun Al-Rashid

Dynamic Error in Strain-Induced Magnetization Reversal of Nanomagnets Due to Incoherent Switching and Formation of Metastable States: A Size-Dependent Study

Modulation of stress anisotropy of magnetostrictive nanomagnets with strain offers an extremely energy-efficient method of magnetization reversal. The reversal process, however, is often incoherent and hence, error-prone in the presence of thermal noise at room temperature. Occurrence of incoherent metastable states in the potential landscape of the nanomagnet can further exacerbate the error. Stochastic micromagnetic simulations at room temperature are used to understand and calculate energy dissipations and switching error probabilities in this important magnetization switching methodology. We find that these quantities have an intriguing dependence on nanomagnet size. Small nanomagnets perform better owing to the fact that they are more resilient to the formation of metastable states and magnetization dynamics in them is more coherent. However, for a fixed stress anisotropy energy density, smaller nanomagnets will also have poorer resilience against thermal instability. Thus, the challenge in straintronics is to maximize the stress anisotropy energy density by developing materials and processes that yield the largest magnetostriction.

Effect of Nanomagnet Geometry on Reliability, Energy Dissipation, and Clock Speed in Strain-Clocked DC-NML

Strain-clocked dipole-coupled nanomagnetic logic is an energy-efficient Boolean logic paradigm whose progress has been stymied by its propensity for high error rates. In an effort to mitigate this problem, we have studied the effect of nanomagnet geometry on error rates, focusing on elliptical and cylindrical geometries. We had previously reported that the out-of-plane excursion of the magnetization vector during switching creates a precessional torque that is responsible for high switching error probability in elliptical nanomagnet geometries. The absence of this torque in cylindrical magnets portends lower error rates, but our simulations show that the error rate actually does not improve significantly compared to elliptical magnets while the switching becomes unacceptably slow. Here, we show that dipole coupled nanomagnetic logic can offer relatively high reliability (switching error probability<10^-8), moderate clock speed (~ 100 MHz) and 2-3 orders of magnitude energy saving compared to CMOS devices, provided the shape anisotropy energy barrier of the magnet is increased to at least ~5.5 eV to allow engineering a stronger dipole coupling between neighboring nanomagnets.Strain-clocked dipole-coupled nanomagnetic logic (DC-NML) is an energy-efficient Boolean logic paradigm whose progress has been stymied by its propensity for high error rates. In an effort to mitigate this problem, we have studied the effect of nanomagnet geometry on error rates, focusing on elliptical and cylindrical geometries. We had previously reported that in elliptical nanomagnets, the out-of-plane excursion of the magnetization vector during switching creates a precessional torque that plays a dual role-it speeds up the switching, but is also responsible for the high switching error probability. The absence of this torque in cylindrical magnets should lower error rates, but our simulations show that the error rate actually does not improve significantly compared with elliptical magnets while the switching becomes unacceptably slow. Here, we show that DC-NML employing elliptical nanomagnets can offer relatively high reliability for NML (switching error probability <;

Voltage controlled core reversal of fixed magnetic skyrmions without a magnetic field.

10^{-8}

Incoherent magnetization dynamics in strain mediated switching of magnetostrictive nanomagnets

), moderate clock speed (

Image Processing With Dipole-Coupled Nanomagnets: Noise Suppression and Edge Enhancement Detection

\sim 100

Energy efficient and fast reversal of a fixed skyrmion two-terminal memory with spin current assisted by voltage controlled magnetic anisotropy

MHz), and two to three orders of magnitude energy saving compared with CMOS devices, provided the shape anisotropy energy barrier of the nanomagnet is increased to at least

Polarized neutron reflectometry study of depth dependent magnetization variation in Co thin film due to strain transfer from PMN-PT substrate

\sim 5.5

An energy efficient memory device based on fixed magnetic skyrmions switched with an electric field

eV to allow engineering a stronger dipole coupling between neighboring nanomagnets.

Binary information propagation in circular magnetic nanodot arrays using strain induced magnetic anisotropy.

Using micromagnetic simulations we demonstrate core reversal of a fixed magnetic skyrmion by modulating the perpendicular magnetic anisotropy of a nanomagnet with an electric field. We can switch reversibly between two skyrmion states and two ferromagnetic states, i.e. skyrmion states with the magnetization of the core pointing down/up and periphery pointing up/down, and ferromagnetic states with magnetization pointing up/down, by sequential increase and decrease of the perpendicular magnetic anisotropy. The switching between these states is explained by the fact that the spin texture corresponding to each of these stable states minimizes the sum of the magnetic anisotropy, demagnetization, Dzyaloshinskii-Moriya interaction (DMI) and exchange energies. This could lead to the possibility of energy efficient nanomagnetic memory and logic devices implemented with fixed skyrmions without using a magnetic field and without moving skyrmions with a current.

Skewed Straintronic Magnetotunneling-Junction-Based Ternary Content-Addressable Memory—Part II

Micromagnetic studies of the magnetization change in magnetostrictive nanomagnets subjected to stress are performed for nanomagnets of different sizes. The interplay between demagnetization, exchange and stress anisotropy energies is used to explain the rich physics of size-dependent magnetization dynamics induced by modulating stress anisotropy in planar nanomagnets. These studies have important implications for strain mediated ultralow energy magnetization control in nanomagnets and its application in energy-efficient nanomagnetic computing devices.