Tunability of Microwave Frequency Using Spin Torque Nano Oscillator by the Generated Oersted Field with Tunable Free Layer

Abstract

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 $\theta$ from $30^{\circ }$ to $90^{\circ }$ as an increment of $30^{\circ }$. For every individual $\theta$ ranging from $30^{\circ }$ to $90^{\circ }$, 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 $\theta$. 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 $\theta$, 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$$GHz for $\theta =90^{\circ }$ with $H_{\mathrm{\text{oe}}}$ as 50$$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.