Zero Field precession and hysteretic threshold currents in spin torque oscillators with tilted polarizer

TL;DR

This paper investigates the behavior of spin torque oscillators with tilted polarizers in zero magnetic field, revealing static and dynamic states, hysteresis, and the conditions for steady precession driven solely by current.

Contribution

It introduces a detailed phase diagram for TP-STOs in zero field, highlighting the effects of tilt angle on static states, precession, and hysteresis, which were not previously characterized.

Findings

Steady precession occurs at small tilt angles (>1 degree) with high currents.

Hysteretic switching between static states is observed over a broad tilt range.

Coexistence of static and dynamic states leads to large hysteresis in threshold currents.

Abstract

Using non-linear system theory and numerical simulations we map out the static and dynamic phase diagram in zero applied field of a spin torque oscillator with a tilted polarizer (TP-STO).We find that for sufficiently large currents, even very small tilt angles (beta>1 degree) will lead to steady free layer precession in zero field. Within a rather large range of tilt angles, 1 degree< beta <19 degree, we find coexisting static states and hysteretic switching between these using only current. In a more narrow window (1 degree<beta<5 degree) one of the static states turns into a limit cycle (precession). The coexistence of static and dynamic states in zero magnetic field is unique to the tilted polarizer and leads to large hysteresis in the upper and lower threshold currents for TP-STO operation.