Voltage-controlled magnetic anisotropy under the electronic structure modulation in quantum wells

TL;DR

This paper investigates how quantum well states influence voltage-controlled magnetic anisotropy in magnetic tunnel junctions, revealing a novel bi-polar VCMA effect linked to quantum well states and Fe-layer parity.

Contribution

It demonstrates that quantum well states significantly modulate VCMA, introducing a new bi-polar VCMA effect dependent on Fe-layer parity, advancing MRAM design strategies.

Findings

A-shaped VCMA curve observed for even Fe layers

Quantum well states contribute to perpendicular magnetic anisotropy

Parity dependence of VCMA linked to quantum well states

Abstract

Voltage-controlled magnetic anisotropy (VCMA) offers an emerging approach to realize energy-efficient magnetization switching in spintronic devices such as magnetic random access memories (MRAMs). Here, we show that manipulating the condensed states, i.e., introducing quantum well (QW) can significantly influence the VCMA in a Cr/Fe-QW/MgAl2O4 based magnetic tunnel junction (MTJ). Only for the MTJ with an even number of Fe atomic layers, we observed a novel A-shaped VCMA curve for a particular QW state, where magnetic anisotropy energy (MAE) reaches a local maximum at zero bias and reduces when applying both positive and negative bias, i.e., a novel bi-polar VCMA effect. Our ab initio calculations demonstrate that the QW states give an additional contribution to perpendicular magnetic anisotropy (PMA), which can explain not only the A-shaped VCMA but also the Fe-layer-number parity dependence of VCMA. The present study suggests that the QW-modulated VCMA should open a new pathway to design VCMA-assisted MRAM.