Reversal of the magnetoelectric effect at a ferromagnetic metal/ferroelectric interface induced by metal oxidation

Zhaojin Chen,Evgeny Y Tsymbal,Lingling Tao,Qiong Yang

doi:10.1038/s41524-021-00679-2

Zhaojin Chen, Evgeny Y Tsymbal + Show 2 more

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https://doi.org/10.1038/s41524-021-00679-2

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Multiferroic materials composed of ferromagnetic and ferroelectric components are interesting for technological applications due to sizable magnetoelectric coupling allowing the control of magnetic properties by electric fields. Due to being compatible with the silicon-based technology, HfO2-based ferroelectrics could serve as a promising component in the composite multiferroics. Recently, a strong charge-mediated magnetoelectric coupling has been predicted for a Ni/HfO2 multiferroic heterostructure. Here, using density functional theory calculations, we systematically study the effects of the interfacial oxygen stoichiometry relevant to experiments on the magnetoelectric effect at the Ni/HfO2 interface. We demonstrate that the magnetoelectric effect is very sensitive to the interface stoichiometry and is reversed if an oxidized Ni monolayer is formed at the interface. The reversal of the magnetoelectric effect is driven by a strong Ni−O bonding producing exchange-split polarization-sensitive antibonding states at the Fermi energy. We argue that the predicted reversal of the magnetoelectric effect is typical for other 3d ferromagnetic metals, such as Co and Fe, where the metal-oxide antibonding states have an opposite spin polarization compared to that in the pristine ferromagnetic metals. Our results provide an important insight into the mechanism of the interfacial magnetoelectric coupling, which is essential for the physics and application of multiferroic heterostructures.

Highlights

Multiferroic materials have drawn much attention due to the magnetoelectric coupling providing new paradigms for electronic devices[1,2]
The control of magnetic properties by an applied electric field rather than a magnetic field or a spin-polarized current requires much less energy[3,4,5], making multiferroics promising for non-volatile memory and logic applications[6,7]
Layered multiferroic structures comprising ferroelectric and ferromagnetic components are most favorable in this regard owing to the significant interfacial magnetoelectric coupling strength, which can be a few orders of magnitude larger than that in the single-phase multiferroics[8,9,10,11], as a result of the strainmediated[12,13,14,15,16] and charge-mediated[17,18,19,20,21,22,23] coupling mechanisms

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Introduction

Multiferroic materials have drawn much attention due to the magnetoelectric coupling providing new paradigms for electronic devices[1,2]. Consistent with our previous work[49], we find that the pristine Ni/HfO2 interface exhibits a “conventional” magnetoelectric effect driven by the depletion (accumulation) of the screening electronic charges, where the interfacial magnetization is enhanced (reduced) for ferroelectric polarization of HfO2 pointing away from (into) the ferromagnetic Ni layer (Fig. 1a, b).

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