Ultralow-current-density and bias-field-free spin-transfer nano-oscillator

TL;DR

This paper demonstrates a spin-transfer nano-oscillator that operates at ultralow current densities without external magnetic fields, enabling more power-efficient and easily integrable microwave sources.

Contribution

It introduces a novel STNO design with MgO-based magnetic tunnel junctions that achieves microwave emission at ultralow currents and zero bias magnetic field, surpassing previous current density benchmarks.

Findings

Microwave emission observed without external magnetic fields.

Critical current density over ten times lower than previous reports.

Potential for better integration with CMOS technology.

Abstract

The spin-transfer nano-oscillator (STNO) offers the possibility of using the transfer of spin angular momentum via spin-polarized currents to generate microwave signals. However, at present STNO microwave emission mainly relies on both large drive currents and external magnetic fields. These issues hinder the implementation of STNOs for practical applications in terms of power dissipation and size. Here, we report microwave measurements on STNOs built with MgO-based magnetic tunnel junctions having a planar polarizer and a perpendicular free layer, where microwave emission with large output power, excited at ultralow current densities, and in the absence of any bias magnetic fields is observed. The measured critical current density is over one order of magnitude smaller than previously reported. These results suggest the possibility of improved integration of STNOs with complementary metal-oxide-semiconductor technology, and could represent a new route for the development of the next-generation of on-chip oscillators.