Charge-Transfer-Induced Interfacial Exchange Coupling at the $\mathrm{Co}/{\mathrm{Bi}\mathrm{Fe}\mathrm{O}}_{3}$ Interface

Charge-Transfer-Induced Interfacial Exchange Coupling at the $Co / {Bi Fe O}_{3}$ Interface

Jianwei Meng, Kai Chen, Emin Mijit, Dongfang Chen, Fadi Choueikani, Zhiqiang Zou, Lingling Wang, Gang Mu, Wenping Geng, Qingyu Kong, Anquan Jiang, Xi-Jing Ning, and Tsu-Chien Weng

Phys. Rev. Applied 12, 044010 – Published 4 October 2019

Abstract

The interplay between ferroelectricity and magnetism in multiferroic materials is of great scientific and technological interest, allowing magnetic control of ferroelectric properties and electric control of magnetic properties through the magnetoelectric coupling from interfacial strain, exchange bias, or charge-transfer process. We report the charge transfer at the $Co / {Bi Fe O}_{3}$ interface from which the interfacial exchange coupling is achieved with the formation of ${Fe}^{2 +}$ . The x-ray linear dichroism and x-ray magnetic circular dichroism results reveal that the strain as well as the exchange coupling $J_{ex}$ in ${Bi Fe O}_{3}$ (BFO) with periodic 109° domains are stronger than that in BFO with 71° domains, resulting in the higher coercive field of $Co / BFO$ with 109° domain samples. The possible electric field control of the charge-transfer process at the $Co / BFO$ interface enables an alternative class of electrically controllable magnetization, exchange bias, and giant magnetoresistive response of spintronic devices.

Received 24 May 2019
Revised 29 July 2019
Corrected 5 January 2023

DOI:https://doi.org/10.1103/PhysRevApplied.12.044010

Physics Subject Headings (PhySH)

Exchange interaction Ferroelectricity Magnetoelectric effect Spintronics Strain Surface & interfacial phenomena

Magnetic multilayers Multiferroics

Condensed Matter, Materials & Applied Physics

Corrections

5 January 2023

Correction: The author name Yimin Mijiti has been changed to Emin Mijit.

Authors & Affiliations

Jianwei Meng ^1,2,3,†, Kai Chen^2,4,5,†, Emin Mijit⁴, Dongfang Chen⁶, Fadi Choueikani⁴, Zhiqiang Zou³, Lingling Wang⁷, Gang Mu⁷, Wenping Geng⁸, Qingyu Kong⁴, Anquan Jiang⁶, Xi-Jing Ning¹, and Tsu-Chien Weng^2,3,*

¹Institute of modern physics, Fudan University, Shanghai 200433, China
²High Pressure for Science & Technology Advanced Research, Shanghai 201203, China
³School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
⁴SOLEIL, l’Orme des Merisiers, St. Aubin, BP48, 91192 Gif sur Yvette Cedex, France
⁵Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
⁶State Key Laboratory of ASIC and system, School of Microelectronics, Fudan University, Shanghai 200433, China
⁷State Key Laboratory of Functional Materials for informatics, Shanghai Institute of Microsystem and information Technology, Chinese Academy of Sciences, Shanghai 200050, China
⁸Science and Technology on Electronic Test and Measurement Laboratory, North University of China, Taiyuan 030051, China

^*wengzq@shanghaitech.edu.cn
^†These authors contributed equally.

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Vol. 12, Iss. 4 — October 2019

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Figure 1
The surface topography and PFM image of ${Bi Fe O}_{3}$ samples. (a) Topography, (b) in-plane PFM image, and (c) out-of-plane PFM image show the periodic 109° stripelike domain structure in BFO/GSO samples. (d) Topography, (e) in-plane PFM image and (f) out-of-plane PFM image indicate the 71° stripelike domain structure in BFO/GSO samples. The insets of (a),(d) show the relationship between the step advance and the domain styles of the BFO film.
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Figure 2
Magnetic hysteresis of $Co / BFO$ samples. (a) Room temperature magnetic hysteresis loops of a single $Co$ layer (open black), $Co / BFO 71$ (open orange), and $Co / BFO 109$ (open blue) heterostructure measured with a magnetic field applied along the [100] direction. (b) The derivative of the magnetization curve of the samples. (c) Evolution of the coercive field H_c with temperature for samples $Co$ (solid black), $Co / BFO 71$ (solid orange), and $Co / BFO 109$ (solid blue) as measured by Quantum Design's Magnetic Property Measurement System. Error bars are smaller than the points.
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Figure 3
X-ray absorption spectroscopy studies on ${Bi Fe O}_{3}$ with 71° and 109° domains. Polarization-dependent $Fe L_{2, 3}$ spectra of BFO/STO (a), BFO/GSO thin films with 109° (b), and 71° (c) type domain with linear polarized x-rays, at T = 4 K. The red and black curves correspond to the polarization of x-rays parallel to OOP and IP directions, respectively. (d) The corresponding XLD (σ^ab - σ^c) with the intensity more reduced in BFO71/GSO. (e) A Schematic drawing of the experimental setup of XLD (left: E||a and E||b, middle: E||ab and E||c) and XMCD (right), using linear or circular polarized x-rays, respectively. (f) The XLD intensity, controlled by the tensile or compressive strain in BFO, follows [1–3cos²θ]/2 with θ the tilted angle of the mean AFM axis from the c axis. Polarization-dependent $Fe − L_{2, 3}$ spectra of BFO/GSO thin films with 109° (g) and 71° (h) type domains at 4 K with circular polarized x-rays parallel or antiparallel with the applied field µ₀H = 6.5 T along the c axis, and the corresponding XMCD (σ⁺–σ⁻) spectra are shown in panel (i), which reveal much stronger dichroism in BFO films with 71° domain walls.
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Figure 4
X-ray absorption spectroscopy studies on $Co / BFO$ with 71° and 109° domains. The $Fe − L_{2, 3}$ spectra of BFO/GSO, $Co O / BFO / GSO$ (a) and $Ta / Co / BFO / GSO$ (b) thin films. The insets of (a),(b) show the schematics of the samples. In (b), the spectra are recorded with circular polarized x-rays parallel (red) or antiparallel (blue) with the applied field µ₀H = 6.5 T in the OOP direction, at T = 4 K, with the corresponding XMCD at the bottom. To compare the relative simulations of $F e^{3 +}$ and ${Fe}^{2 +}$ from the atomic multiplet, calculations are also listed at the top. (c) Oxygen K edge XAS spectra from BFO/GSO and $Ta / Co / BFO / GSO$ at T = 4 K. The spectra for BFO/GSO are roughly divided into $Fe$ 3d, Bi 6sp, and $Fe$ 4sp orbital character regions, while for $Co / BFO / GSO$ , the $O$ K edge spectra are roughly divided into $Co$ 3d and $Co$ 4sp, and the Bi 6sp peak disappears.
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Physical Review Applied

Charge-Transfer-Induced Interfacial Exchange Coupling at the Co/BiFeO3 Interface

Jianwei Meng, Kai Chen, Emin Mijit, Dongfang Chen, Fadi Choueikani, Zhiqiang Zou, Lingling Wang, Gang Mu, Wenping Geng, Qingyu Kong, Anquan Jiang, Xi-Jing Ning, and Tsu-Chien Weng

Phys. Rev. Applied 12, 044010 – Published 4 October 2019

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Charge-Transfer-Induced Interfacial Exchange Coupling at the $Co / {Bi Fe O}_{3}$ Interface