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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]

Abstract The objective of the experimental work is to enhance the machining capability of electrical discharge machining by suspending equal proportion of metal powders such as, molybdenum, nickel, and chromium in EDM 30 oil. Three different control factors such as peak current, pulse on time and powder concentration were varied to analyze the response factors namely material removal rate, surface roughness and radial overcut. The cause of powders concentration on material removal rate (MRR), surface roughness (SR), and radial overcut (ROC) have been investigated. An electron dispersive spectroscopy was utilized to investigate the surface revealed the deposition of nickel and chromium in the machined surface. Machined surface was focused to atomic force microscopy and scanning electron microscopy. Analysis of variance (ANOVA) results showed that peak current is the foremost factor in affecting MRR, SR and ROC.

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.

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]

Dipole-exchange spin waves (SWs) propagation in the air gap and bicomponent magnonic waveguides (BMWs) encompassed with alternating $SM$ and $N$ stripes based on different saturation magnetization ($M_{s}$) is studied through micromagnetic simulation. The air gaps MWs (AMWs) exhibit the transmission bands in the range ≈3–10 GHz as a result of inhomogeneous demagnetization field around the $N$ stripes (air gaps), where the magnetostatic coupling helps to propagate the SWs in entire waveguides with low group velocity $v_{g} \approx 28$ –380 m/s. By incorporating two different $M_{s}$ , magnetic materials in both $SM$ and $N$ stripes form BMWs enhancing the transmission bands from narrow to the wide range which is ≈14–60 GHz due to large exchange coupling at the interfaces. It increases the intercoupling between neighboring stripes, which reduces the energy loss of SWs that can be propagated throughout the entire waveguide with large group velocity $v_{g} \approx 8500$ –10600 m/s. The design of AMWs and BMWs would be suitable to construct an efficient signal processing device with high group velocity and wide transmission bands depending on periodicity and saturation magnetization present in the MWs. [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]

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]

We present the possibility of tuning the spin-wave band structure, particularly the bandgaps in a nanoscale magnonic antidot waveguide by varying the shape of the antidots. The effects of changing the shape of the antidots on the spin-wave dispersion relation in a waveguide have been carefully monitored. We interpret the observed variations by analysing the equilibrium magnetic configuration and the magnonic power and phase distribution profiles during spin-wave dynamics. The inhomogeneity in the exchange fields at the antidot boundaries within the waveguide is found to play a crucial role in controlling the band structure at the discussed length scales. The observations recorded here will be important for future developments of magnetic antidot based magnonic crystals and waveguides. [ABSTRACT FROM AUTHOR]

We investigate nonlinear localized magnetic excitations in a one-dimensional bicomponent magnonic crystal under a periodic magnetic field of spatially varying strength. The governing Landau-Lifshitz equation is transformed into a variable coefficient nonlinear Schrödinger (VCNLS) equation using stereographic projection. In general, the VCNLS equation is nonintegrable and by using Painlevé analysis, we obtain necessary conditions for the VCNLS equation to pass the Weiss-Tabor-Carnevale Painlevé test. A sufficient integrability condition is obtained by further exploring a transformation, which can map the VCNLS equation into the well-known standard nonlinear Schrödinger equation. The transformation builds a systematic connection between the solution of the standard nonlinear Schrödinger equation and VCNLS equation. The results show that the excitation of magnetization in the form of a soliton exists on the oscillatory background with a structure similar to the form of spin Bloch waves. Such a solution exists only when certain conditions on the coefficient of the VCNLS equation are satisfied. To corroborate the analytical results, we performed the numerical simulation by solving the governing VCNLS equation with integrability conditions using the split step Fourier method and the result agrees well with analytical results, and it suggests a way to control the dynamics of magnetization in the form of solitons by an appropriate spatial modulation of the nonlinearity coefficient in the governing VCNLS equation, which depends on the ferromagnetic materials which form the bicomponent magnonic crystal. [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]