Spin-torque oscillation in large size nano-magnet with perpendicular magnetic fields

Abstract

DC current induced magnetization reversal and magnetization oscillation was observed in 500 nm large size Co 90 Fe 10 /Cu/Ni 80 Fe 20 pillars. A perpendicular external field enhanced the coercive field separation between the reference layer (Co 90 Fe 10 ) and free layer (Ni 80 Fe 20 ) in the pseudo spin valve, allowing a large window of external magnetic field for exploring the free-layer reversal. The magnetization precession was manifested in terms of the multiple peaks on the differential resistance curves. Depending on the bias current and applied field, the regions of magnetic switching and magnetization precession on a dynamical stability diagram has been discussed in details. Micromagnetic simulations are shown to be in good agreement with experimental results and provide insight for synchronization of inhomogenieties in large sized device. The ability to manipulate spin-dynamics on large size devices could prove useful for increasing the output power of the spin-transfer nano-oscillators (STNOs).Spin-polarized currents can be harnessed to manipulate magnetization and excite oscillation via the spin transfer torque (STT) effect, and are utilized in the application of MRAM [1,2] and spin-transfer nano-oscillators (STNOs) [3,4] . STNOs have the advantages that their frequencies are highly tunable by current and magnetic field over a range from 2 a few GHz to 40 GHz. [3,5] Furthermore, the nanometer sized devices are among the smallest microwave oscillators yet developed [6] and their compatibility with standard silicon processing opens the possibility for on-chip applications. [7,8] However, the bottlenecks for the widespread application of STNOs lies in the enhancement of the output power above the current limit of ~ 0.5µW. [9] It has been suggested that two nano-contact STNOs in close proximity could mutually phase-lock and increase the output power; however phase-locking of more than two STNOs remains technologically challenge. [10][11][12][13][14] Instead of putting an array of STNOs nano-magnets together, we propose to make use of larger sized magnets in the hope that synchronization of multiple domains could lead to higher output power, and firstly we demonstrated that spin-transfer torque can be used to efficiently induce magnetization switching and oscillation in 500 nm large size devices. For large size device, our simulation results have shown that the non-uniform oscillations tend to synchronize with each other and generate coherent oscillation. In addition, large sized nano-magnets can be fabricated more cost-effectively through photolithography rather than using electron beam lithography. 3The magnetic multilayer was synthesized by sputtering in a Biased Target Ion Beam Deposition system (BTIBD). The deposition details can be found elsewhere. [15] The complete structure of the multilayer is SiO 2 (substrate)/20nm Ru/2.2nm Co 90 Fe 10 (reference layer)/5nm Cu/6.5nm Ni 80 Fe 20 (free layer)/5nm Ru/Ti 5nm/Au 25nm. A magnetoresistance (MR) of ~1.2% was measured in the pseudo spin-valve continuous f...

Electric-Field-Controlled Nonvolatile Magnetization Rotation and Magnetoresistance Effect in Co/Cu/Ni Spin Valves on Piezoelectric Substrates

“…Consistent with the results at room temperature (see Figure S3, Supporting Information), the MEA directions of the Co and Ni films at P i state stay in the [100] direction at 80 K, and the coercive fields of Co and Ni films are about ±250 and ±510 Oe, respectively. It is noted that the resistance of our spin valve is higher than that of the previous reported all-metal spin valves (10 –8 to >10 Ω), − which may be owing to the polycrystalline nature of our sample, the contribution from current-in-plane resistance, and/or the possible weak oxidization of the 3d metals in the spin valve.…”

Voltage-input spintronic oscillator based on competing effect for extended oscillation regions

“…1, (i) only VDD,STT is applied, (ii) only VDD,SOT is applied, and (iii) both VDD,STT and VDD,SOT are applied, in which we have observed qualitatively different frequency trend and oscillation patterns. Therefore, the oscillation in the VICSO is unlikely originated from the synchronization [61,62] between the STT-and SOTinduced oscillations.…”

Influence of magnetic structure on the performance of twisted skyrmion-based nano-oscillator

“…ξ which represents the strength of the perpendicular spin torque is set to 0.1. u indicates the spin polarized electron velocity, denoted as u = [(γℏP) /2µ 0 eM s ] J, where ℏ is the Planck constant, P is the spin polarization with fixed as 0.4 [50], µ 0 is the permeability, M S is the saturation magnetization. J and e are the current density and the electron charge, respectively [51][52][53][54]. The magnetic material of the free layer is Co [54] and the parameters are set as: saturation magnetization M S = 5.8 × 10 5 A m −1 , perpendicular magnetic anisotropy constant…”