Spin torque nano-oscillators with a perpendicular spin polarizer

Abstract

We present an overview in the understanding of spin-transfer torque (STT) induced magnetization dynamics in spintorque nano-oscillator (STNO) devices. The STNO contains an in-plane (IP) magnetized free layer and an out-of-plane (OP) magnetized spin polarizing layer. After a brief introduction, we first use mesoscopic micromagnetic simulations, which are based on the Landau-Lifshitz-Gilbert equation including the STT effect, to specify how a spin-torque term may tune the magnetization precession orbits of the free layer, showing that the oscillator frequency is proportional to the current density and the z-component of the free layer magnetization. Next, we propose a pendulum-like model within the macrospin approximation to describe the dynamic properties in such type of STNOs. After that, we further show the procession dynamics of the STNOs excited by IP and OP dual spin-polarizers. Both the numerical simulations and analytical theory indicate that the precession frequency is linearly proportional to the spin-torque of the OP polarizer only and is irrelevant to the spin-torque of the IP polarizer. Finally, a promising approach of coordinate transformation from the laboratory frame to the rotation frame is introduced, by which the nonstationary OP magnetization precession process is therefore transformed into the stationary process in the rotation frame. Through this method, a promising digital frequency shift-key modulation technique is presented, in which the magnetization precession can be well controlled at a given orbit as well as its precession frequency can be tuned with the co-action of spin polarized current and magnetic field (or electric field) pulses.

Magnetic vortex gyration mediated by point-contact position*

“…Moreover, the point-contact is not located at the disk center and the distance between its center and the center of the disk is d. In order to conveniently demonstrate the influence of the point-contact position on the MV gyration, we define R d = d/R in this work. Magnetization simulation calculation is performed by OOMMF based on Landau-Lifshitz-Gilbert (LLG) equation with spin-transfer-torque (STT) and Oersted field induced by the current, [18,19,25]…”

“…[3][4][5][6][7][8][9][10] In order to apply MV to new spintronic devices, the key point is to control the dynamic properties of MV such as the polarity reversal, chirality reversal, and gyration. [4,[11][12][13][14][15][16][17][18][19] Recently, we investigated the polarity reversal mediated by a spin-polarized current in a confined geometry, finding that not only the MV can be easier triggered but also the polarity can be reversed with a lower current density and using less time if the point-contact is not designed in the nanodisk center. [20,21] Furthermore, our research found that the position and the size of point-contact can control the eigenfrequency of MV gyration.…”

Voltage-driven gigahertz frequency tuning of spin Hall nano-oscillators

“…Figure 4f shows the 𝐼 gh according to the 𝑉 : . Here, the 𝐼 gh values are extracted by a linear fit of the inverse of the PSD integral (Supplementary Note 4) [48].…”

Enhancement of spin-orbit torque efficiency by tailoring interfacial spin-orbit coupling in Pt-based magnetic multilayers

“…Spin-orbit torques [1][2][3][4][5][6][7][8] in heavy metal/ferromagnet (HM/FM) systems have become a powerful approach to achieving a pure current control of magnetization switch for building an energy-efficient SOT-magnetoresistive random-access memory (SOT-MRAM) [9] and excitation of coherent spin waves for magnon-based logic devices [10,11] or spin synchronization-based neuromorphic computing [12][13][14].…”