Low-frequency and shot noises in CoFeB/MgO/CoFeB magnetic tunneling junctions

TL;DR

This study investigates low-frequency and shot noises in CoFeB/MgO/CoFeB magnetic tunneling junctions, revealing magnetic fluctuations as the source of 1/f noise and spin-dependent activation of RTN, with shot noise indicating coherent tunneling.

Contribution

It provides new insights into the magnetic fluctuation origins of 1/f noise and the spin-dependent nature of RTN in magnetic tunnel junctions.

Findings

1/f noise mainly caused by magnetic fluctuations.

RTN is enhanced in the antiparallel magnetic configuration.

Shot noise indicates spin-dependent coherent tunneling.

Abstract

The low-frequency and shot noises in spin-valve CoFeB/MgO/CoFeB magnetic tunneling junctions were studied at low temperature. The measured 1/f noise around the magnetic hysteresis loops of the free layer indicates that the main origin of the 1/f noise is the magnetic fluctuation, which is discussed in terms of a fluctuation-dissipation relation. Random telegraph noise (RTN) is observed to be symmetrically enhanced in the hysteresis loop with regard to the two magnetic configurations. We found that this enhancement is caused by the fluctuation between two magnetic states in the free layer. Although the 1/f noise is almost independent of the magnetic configuration, the RTN is enhanced in the antiparallel configuration. These findings indicate the presence of spin-dependent activation of RTN. Shot noise reveals the spin-dependent coherent tunneling process via a crystalline MgO barrier.