Self-oscillations induced by self-induced torque in magnetic double tunnel junction

TL;DR

This work investigates self-oscillations in a magnetic double tunnel junction (MDTJ) induced by self-induced torque (SIT) within the Landau-Lifshitz-Gilbert-Slonczewski framework, including field-like torque (FLT). Using adaptive Runge-Kutta simulations of a macrospin, SIT is shown to sustain zero-field GHz precession around $+\hat{z}$, whereas without SIT the magnetization simply switches. The presence and sign of FLT markedly influence oscillator performance: negative ${\beta}$ enhances frequency tunability, power, and Q-factor with increasing current, while positive ${\beta}$ can suppress oscillations beyond a critical current. The frequency follows an analytic-like fit $f=\frac{\gamma}{2\pi\alpha} H_s (1+\mu B)$, and the system remains robust to thermal noise with modest shifts in frequency and broadened oscillation range, highlighting SIT as a viable mechanism for field-free GHz STNOs with tunable characteristics.

Abstract

Self-oscillations of the magnetization due to self-induced torque (SIT) in a magnetic double tunnel junction that consists of perpendicularly polarized, pinned and free layers is investigated along with the field-like torque (FLT). The associated Landau-Lifshitz-Gilbert-Slonczewski equation is numerically analysed to exhibit the oscillations of magnetization driven by the current. From the numerical analysis, we show that the SIT is essential to generate oscillations in the order of GHz and without it the magnetization reaches steady state after exhibiting switching. Without FLT, the frequency of the oscillations decreases with the current while the power of oscillations increases. In the presence of the negative strength of the FLT the power spectral density confirms that the frequency, power and the Q-factor increase with the current. Also the tunability range and the rate at which the frequency enhances increase with the magnitude of the FLT.

Figures (10)

• Figure 1: Schematic diagram of a system of magnetic double tunnel junction. The free layer in the middle is tunnel coupled with a pinned layer at left and normal metal layer at right.
• Figure 2: Oscillation of the magnetization components $m_x$, $m_y$, and $m_z$ in the (a-b) absence and (d-f) presence of the SIT corresponding to the currents $I$ = 5, 10, and 15 mA.
• Figure 3: Trajectory of the magnetization without (blue) and with (red) SIT for $I$ = 15 mA and $\beta$ = 0.
• Figure 4: (a) Frequency and (b) range and precession angle $\theta_p$ of oscillations with respect to the current. (c) PSD for the currents $I$ = 5, 10, and 15 mA. Here, $\beta$ = 0.
• Figure 5: (a) Frequency and (b) range and angle of precession $\theta_p$ of the oscillations for $\beta$ = -0.6 (blue), -0.3 (red), 0 (magenta), 0.3 (green), and 0.6 (brown) against current. (c) Frequency and (d) range and angle of precession $\theta_p$ of the oscillations for the currents $I$ = 4 mA (re), 8 mA (blue), 12 mA (magenta), 16 mA (green), 20 mA (brown), and 24 mA (orange) against the strength of FLT $\beta$. The open circles in (a) correspond to the frequency of oscillations obtained from Eq.\ref{['freq']}.