Anomalous switching pattern in the ferrimagnetic memory cell

TL;DR

This paper investigates the unique switching behaviors of ferrimagnetic tunnel junctions in MRAM, revealing how composition and compensation points influence switching dynamics and offering insights for improved device design.

Contribution

It uncovers the anomalous switching patterns in FiM-MTJs, including the effects of Gd content and compensation points on switching currents and dynamics.

Findings

Switching from parallel to antiparallel state is limited by a small window.

Reducing magnetoresistance ratio suppresses current variation.

Polarity reversal occurs at the angular momentum compensation point.

Abstract

Replacing the ferromagnet with ferrimagnet (FiM) in the magnetic tunnel junction (MTJ) allows faster magnetization switching in picoseconds. The operation of a memory cell that consists of the MTJ and a transistor requires reversable magnetization switching. When a constant voltage is applied, we find that the spin-transfer torque can only switch the FiM-MTJ from parallel to antiparallel state. This stems from the small switching window of FiM and the dynamic resistance variation during the magnetization switching. We find the resulting current variation can be suppressed by reducing the magnetoresistance ratio. Furthermore, we demonstrate that the switching window can be expanded by adjusting the amount of Gd in FiM. We predict that the polarity of both switching current (Jc,switch) and oscillation current (Jc,osc) reverses at the angular momentum compensation point but not the magnetization compensation point. This anomalous dynamic behavior is attributed to the different physical nature of magnetization switching and oscillation in FiM, which must be considered when designing FiM-based MRAM.