Backhopping effect in magnetic tunnel junctions: comparison between theory and experiment

TL;DR

This paper investigates the backhopping effect in magnetic tunnel junctions caused by spin-transfer-torque, comparing experimental results with macrospin model simulations to understand the influence of barrier thickness and bias voltage on magnetic switching behavior.

Contribution

It provides a combined experimental and theoretical analysis of backhopping in MTJs, highlighting the role of barrier thickness and torque components in non-deterministic switching.

Findings

Backhopping occurs when current favors parallel magnetization.

Thinner barriers (<0.95 nm) suppress backhopping.

Numerical simulations match experimental non-deterministic switching.

Abstract

We report on the magnetic switching and backhopping effects due to spin-transfer-torque in magnetic tunnel junctions. Experimental data on the current-induced switching in junctions with MgO tunnel barrier reveal a random back-and-forth switching between the magnetization states, which appears when the current direction favors the parallel magnetic configuration. The effect depends on the barrier thickness $t_b$, and is not observed in tunnel junctions with very thin MgO tunnel barriers, $t_b$ $<$ 0.95 nm. Switching dependence on the bias voltage and barrier thickness is explained in terms of the macrospin model, with the magnetization dynamics described by the modified Landau-Lifshitz-Gilbert equation. Numerical simulations indicate that the competition between in-plane and out-of-plane torque components can result at high bias voltages in a non-deterministic switching behavior, in agreement with experimental observations. When the barrier thickness is reduced, the overall coupling between the magnetic layers across the barrier becomes ferromagnetic, which suppresses the backhopping effect.