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The current-induced magnetization precession dynamics provoked by the spin transfer torque (STT) in a spin valve device i.e. tri-layer device (commonly spin torque nano oscillator (STNO)) is investigated numerically by solving the governing Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation. In this study, we have devised an STNO device made of EuO-based ferromagnetic alloy in free and fixed magnetic layers. The copper acts as a nonmagnetic spacer. Here, we have introduced the current induced Oesterd field (CIOF), which is generated when a spin-polarized current passes through the STNO device. In the device, we have tuned the free layer angle θ from 3 0 ∘ to 9 0 ∘ as an increment of 3 0 ∘ . For every individual θ ranging from 3 0 ∘ to 9 0 ∘ , the generated Oersted field's strength can be altered by increasing the STNO device's diameter. Henceforth, it is apparent that the frequency tunability is achieved in the device for all the values of θ. The frequency and power of the device depend entirely on the material's saturation magnetization, which inherently reflects the current density and coherence of spin-polarized DC. From the results, it is apparent that for a particular θ , the frequency keeps increasing with the eventual decrease in power when we increase the strength of the Oersted field from 10 kA/m to 50 kA/m. By doing so, the maximum frequency can be tuned up to 212 GHz for θ = 9 0 ∘ with H oe as 50 kA/m. The high frequency emitted by the device acts as a linchpin ingredient, as well as a launch pad element in much of scientific and technological point of view. It paves way for a new route in the areas such as high capacity, high precision, high density as well as the sensing applications. [ABSTRACT FROM AUTHOR]

The oscillatory interlayer exchange coupling (OXC) between ferromagnetic layers sandwiched by non-magnetic spacer layers plays a significant role in spintronic device function. In this work, the effect of OXC on the current-induced magnetization switching process in four different pentalayer nanopillar alloys is numerically investigated by solving the dynamical equation governed by the Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation. The four nanopillars consist of four ferromagnetic alloys, CoPt, CoFeB, Fe 85 B 13 Ni 2 and EuO, which serve as pinned layers and free layers, with copper forming a spacer layer between all the layers. The critical current density required to switch the magnetization of the free layer is computed for all the devices and the values are 0.6 × 10 11 Am - 2 , 1.31 × 10 11 Am - 2 , 2.24 × 10 11 Am - 2 , 3.27 × 10 11 Am - 2 for CoPt, CoFeB, Fe 85 B 13 Ni 2 and EuO device, respectively. Then we studied how the thickness of the Cu layer influences the OXC field. Furthermore, we investigated the effect of Cu layer thickness on critical current density and magnetization switching time for all the four devices by numerically solving the LLGS equation and they exhibit oscillating behaviour. We can reduce the critical current density and switching time substantially by controlling the OXC field acting on the free layer and choosing the magnetic material having low saturation magnetization as the free layer. The OXC field is optimised by fixing the Cu spacer thickness from 1.7 to 1.9 nm in the pentalayer nanopillar device. [ABSTRACT FROM AUTHOR]

We investigated the influence of oscillatory interlayer exchange coupling (OXC) on spin transfer torque (STT)-assisted magnetization switching in the pentalayer nanopillar structure. The impact of OXC between the ferromagnetic layers in the pentalayer nanopillar is realised by solving the associated governing equation, namely Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. First, we calculated the critical current density needed to switch the magnetization of the free layer in the absence of OXC by analytically solving the LLGS equation and its value is J c = 0.46 × 10 11 A m - 2 . Then, we studied the influence of thickness of the spacer layer on the OXC field term and how it affects the critical current density and magnetization switching behaviour by numerical simulations of LLGS equation. By controlling OXC, we reduce critical current density and magnetization switching time from peak values to 86% and 82%, respectively, which is accomplished by constructing a multilayer with optimal spacer layer thickness of 1.7 to 1.9 nm. This work paves a potential way for practical implementation of STT-based MRAMs, nano-oscillators, and logic devices. [ABSTRACT FROM AUTHOR]

The current-driven magnetization precession dynamics stimulated by Spin-Transfer Torque (STT) in a trilayer spin-valve device (typically Spin-Torque Nanooscillator (STNO)) is numerically investigated by solving the Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation. We have devised four STNO devices made of ferromagnetic alloys such as CoPt, CoFeB, Fe 8 5 B 1 3 Ni2 and EuO, which act as free and fixed layers. Here, copper acts as a nonmagnetic spacer for all the devices. In this work, we have introduced the current-induced Oersted field, which is generated when a spin-polarized current passes through the device. The generated Oersted field strength is varied by increasing the diameter of the STNO device. Frequency tunability is achieved in all the four devices, whereas the power of the individual device reduces. The frequency and power of the devices depend entirely on the saturation magnetization of the material, which inherently reflects in the current density and the coherence of the spin-polarized DC. In all devices, the frequency increases, whereas the power decreases by increasing the strength of the Oersted field. Among the four devices, the maximum frequency can be tuned up to 104 GHz with 40 nm device diameter, which is obtained for EuO material. This opens a promising source and paves a glittering future for the nanoscale spintronic devices. [ABSTRACT FROM AUTHOR]

The effect of biquadratic coupling on spin transfer torque-assisted magnetization switching in the pentalayer nanopillar device is studied by numerically solving the magnetization switching dynamics of the free layer governed by the Landau- Lifshitz-Gilbert-Slonczewski (LLGS) equation. Magnetization switching time in the absence of biquadratic coupling for an applied current density of 10 × 1011Am− 2 is 186 ps. Biquadratic coupling arises due to the uncorrelated roughness in the ferromagnetic layers and it reduces the switching time to 160 ps. Further, the impact of the period of roughness and spacer layer thickness on switching time are studied. [ABSTRACT FROM AUTHOR]

Dipole-exchange spin waves (SWs) propagating in a 1-D magnonic waveguide embedded with different orientations of triangular antidots are investigated through the micromagnetic simulation. The dipole-exchange SW propagation is affected due to the effect of changing the triangular antidots orientation. This leads to reduction in the number of forbidden bands and their gap width in the magnonic waveguide. The SW characteristics are interpreted by plotting frequency dispersion curves and analyzing the power and phase distribution profile (PPDP) and static demagnetization field profile to substantiate the occurrence of bandgaps. The number of forbidden bands and their gap width get reduced due to the formation of symmetric and antisymmetric modes, and it will be further clarified by the PPDPs. For θ = 0°, four wide bandgaps are recorded; I and II bandgaps are due to symmetric modes, whereas the remaining gaps are due to antisymmetric modes. From θ = 0° to 90°, the number of forbidden bands is reduced from 4 to 2 because of the inhomogeneous distribution of the internal field introduced by the presence of triangular array antidots in the transverse direction, and it is confined via the static demagnetization field. The way to develop magnonic antidot-based waveguide for SW filter applications is paved by opening, closing, and tuning of the gap width. This can be effectively brought about by changing the orientation of triangular antidots. [ABSTRACT FROM AUTHOR]

In this paper, we theoretically devised a spin torque nano-oscillator (STNO) with tilted polarizer (TP) with the help of two independent variables ( \beta and \theta ). The spin torque induced magnetization precession dynamics is studied numerically by solving the governing Landau–Lifshitz–Gilbert–Slonczewski equation. The TP STNO free layer precession frequency is determined by varying TP angle ( \beta ) from 0° to 90°. For a particular value of \beta , we can vary ( \theta /GHz/mA2 is obtained for \beta =60 ^\circ and \theta =90 ^\circ with the applied current density of 10\times 10^10 Am−2. Moreover, our results allow great freedom in choosing the detailed layer structure of the TP STNO and these findings pave a new route for the implementation of nanoscale microwave sources for future generation integrated electronics. [ABSTRACT FROM AUTHOR]

The spin transfer torque assisted magnetization switching in a pentalayer nanopillar device is theoretically studied for different biasing configurations. The magnetization switching time is calculated for three different configurations (standard(no biasing), pinned layer biasing and free layer biasing), by numerically solving the governing dynamical Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation. The corresponding switching time for an applied current density of 3 × 10 11 Am − 2 is about 0.296 ns, 0.195 ns, and 0.108 ns respectively. Pinned layer biasing and free layer biasing increase the magnetization switching speed significantly. Reduction of switching time in the pinned layer biasing is due to the enhancement of spin transfer torque, whereas in the free layer biasing it is due to an additional magnetic torque which arises due to an applied magnetic field. The fastest magnetization switching is achieved for the free layer biasing configuration. [ABSTRACT FROM AUTHOR]

Nonlinear localized magnetic excitations in 1-D bicomponent magnonic crystal are investigated under periodic magnetic field of spatially varying strength with spin current. The governing modified Landau–Lifshitz equation with spin current is transformed into the variable coefficient nonlinear Schrödinger (VCNLS) equation using a stereographic projection. In general, the VCNLS equation is nonintegrable and by using similarity transformation technique, the VCNLS equation is reduced into the standard NLS equation with certain integrability conditions. A systematic connection between the solution of VCNLS and NLS equations is established. The solution of VCNLS equation is obtained using the solution of the NLS equation. The excitation of magnetization is in the form of solitons on the oscillatory background with structure similar to the form of spin Bloch waves, and in addition, the spin current controls the soliton velocity. The velocity of soliton is directly proportional to the strength of current density and inversely proportional to the average saturation magnetization value, which is the value of saturation magnetization of the composite material at the interface of the two ferromagnetic materials, which are used to form the bicomponent magnonic crystal. [ABSTRACT FROM AUTHOR]

The impact of orange peel coupling on spin current induced magnetization switching in a Co/Cu/Ni-Fe nanopillar device is investigated by solving the switching dynamics of magnetization of the free layer governed by the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. The value of the critical current required to initiate the magnetization switching is calculated analytically by solving the LLGS equation and verified the same through numerical analysis. Results of numerical simulation of the LLGS equation using Runge-Kutta fourth order procedure shows that the presence of orange peel coupling between the spacer and the ferromagnetic layers reduces the switching time of the nanopillar device from 67 ps to 48 ps for an applied current density of 4 × 1012Am-2. Also, the presence of orange peel coupling reduces the critical current required to initiate switching, and in this case, from 1.65 × 1012Am-2 to 1.39 × 1012Am-2. [ABSTRACT FROM AUTHOR]

Abstract: Magnetization switching dynamics in FePt/Au/FePt nanopillar, induced by spin-transfer torque is investigated by solving the Landau–Lifshitz–Gilbert–Slonczewski equation. The switching of magnetization occurs in the device, above a threshold current density of , which agrees well with the previously reported experimentally measured value. This further reduces to , when there is interface anisotropy in the free FePt layer, whose presence has been identified recently through scanning tunneling microscopy images and X-ray magnetic circular dichroism. The interface anisotropy also reduces the switching time from 15.59ps to 9.56ps when the device having a free FePt layer of thickness 1.5nm is operated with a current density of . [Copyright &y& Elsevier]

Current driven magnetization switching dynamics induced by spin-transfer torque in CoPt/Au/CoPt nanopillar device with interface anisotropy is investigated by solving the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation numerically. The switching of magnetization in the free layer CoPt/Au/CoPt nanopillar with a thickness of 3 nm occurs above the threshold current density of 0.84×108A/cm2. This reduces to 0.30×108A/cm2 when the free CoPt layer of the device has interface anisotropy in it. The presence of interface anisotropy also reduces the magnetization switching time from 8.4 ps to 3.1 ps when the device is operated by a current with a density of 2.78×108A/cm2. [ABSTRACT FROM AUTHOR]

Abstract: Precessional switching of magnetization in CoPt and FePt nanofilms is investigated by solving the Landau–Lifshitz–Gilbert (LLG) equation analytically and numerically. Switching in these films occurs only above a critical value of the magnetic field, and it further depends on the magnetocrystalline anisotropy and saturation magnetization of the film. The presence of magnetic surface anisotropy in these films reduces the switching time significantly. Also, the switching time in the case of Pt-alloys of Co and Fe is low compared to that in the case of pure Co and Fe films. [Copyright &y& Elsevier]

This work investigates theoretically the possibility of a dual-barrier magnetic tunnel junction (MTJ) to act as a spin-torque oscillator (STO) which could produce microwaves. We have identified the parameters that control the frequency of oscillations and tuned them to get a maximum frequency. To improve the output power and reduce the distortions, phase locking the STO through external alternating current is done. It is found that the synchronisation occurs rapidly leading to a reduced response time, which is a significant result. Interestingly, magnetisation dynamics becomes chaotic for specific choice of parameters and the period doubling bifurcation is studied to explore the route to chaos. [ABSTRACT FROM AUTHOR]

Reprogrammable microwave properties based on magnetic nanostructures are of great interest for future information-processing technologies in the GHz frequency range. Tunable microwave properties are typically obtained by varying the bias magnetic field, which, however, hinders the device integration capability at the nanoscale. Here, we show a route for bias-field-free giant tunability of microwave properties based on isolated and dipolar coupled networks of multilayer rhomboid nanomagnets. A comprehensive investigation of multilayers beyond trilayer and various complex networks of them are carried out using micromagnetic simulations. The giant tunability of the microwave properties has been attributed to the strong dipolar field variations associated with different remanent states which can be reconfigured with a nanosecond pulse field. We have also presented an approach for realization of an artificial 3D antiferromagnetic crystal. These results have potential applications in fast reprogrammable and energy-efficient microwave devices which operate without any bias magnetic field. [ABSTRACT FROM AUTHOR]