Size-dependent enhancement of passive microwave rectification in magnetic tunnel junctions with perpendicular magnetic anisotropy

TL;DR

This study demonstrates that reducing the size and thickness of magnetic tunnel junctions with perpendicular magnetic anisotropy significantly enhances their microwave rectification efficiency, improving spintronic RF detector performance.

Contribution

It reveals size and thickness-dependent effects on rectification in PMA MTJs, optimizing their design for better RF energy harvesting and detection.

Findings

Rectified voltage increases 5-6 times when diameter decreases from 150nm to 20nm.

Doubling of enhancement occurs when free layer thickness is reduced from 1.8nm to 1.6nm.

The enhancement is due to changes in effective anisotropy and MTJ resistance.

Abstract

Spintronic rf detectors were demonstrated, recently, for energy harvesting and wireless communication at low input power. Here we report on the optimization of the rectified output dc voltage using magnetic tunnel junctions (MTJ) with strong perpendicular anisotropy (PMA) of both the polarizing and the free layer. The magnetization of the polarizing layer is fixed out of plane, while the free layer thickness is adjusted so that its magnetization orientation changes from in plane to out of plane. The rectification dc output voltage lies in the mV range for moderate rf powers, with a signal to noise ratio of 10 to 100 for Prf = -25dBm. It shows a strong dependence on the dimensions of the MTJ: it increases by a factor of 5 to 6 when reducing the diameter from 150nm to 20nm. This enhancement can be doubled when reducing the FL thickness from 1.8nm to 1.6nm. This dimensional enhancement is attributed to the change of the effective anisotropy of the excited free layer, and the MTJ resistance. The results are of interest for the design of spintronic based rf detectors with optimized sensitivity.