Intrinsic spin noise in MgO magnetic tunnel junctions

TL;DR

This paper analyzes intrinsic spin noise sources in MgO magnetic tunnel junctions, identifying nuclear spins and vacancies as key contributors affecting sensor noise across different frequency ranges.

Contribution

It introduces a detailed analysis of nuclear and vacancy spin noise in MgO junctions, highlighting their spectral characteristics and potential for spatial spin mapping.

Findings

Nuclear spin noise peaks in the MHz range.

Vacancy-induced noise dominates in the GHz range.

Noise levels comparable to 1/f noise in submicron devices.

Abstract

We consider two intrinsic sources of noise in ultra-sensitive magnetic field sensors based on MgO magnetic tunnel junctions, coming both from $^{25}$Mg nuclear spins ($I=5/2$, 10% natural abundance), and S=1 Mg-vacancies. While nuclear spins induce noise peaked in the MHz frequency range, the vacancies noise peaks in the GHz range. We find that the nuclear noise in submicron devices has a similar magnitude than the $1/f$ noise, while the vacancy-induced noise dominates in the GHz range. Interestingly, the noise spectrum under a finite magnetic field gradient may provide spatial information about the spins in the MgO layer.