The discovery opens the way to exciting new uses of vdW materials, with insertion of protons an important new technique, now available for the wider 2D materials research community.

The study was led by FLEET researchers at RMIT, in an ongoing collaboration with FLEET partner organisation High Magnetic Field Laboratory, Chinese Academy of Sciences (CAS).

TUNING INTERLAYER FORCES IN VDW MATERIALS

Van der Waals materials, of which graphite is the most famous, are made of many 2D layers held together by weak, electrostatic forces.

Individual layers of vdW materials can be isolated individually, such as the famous Scotch tape method of producing graphene, or stacked with other materials to form new structures.

"But the same weak interlayer forces that make vdW materials so easy to separate also limit these materials' applications in future technology," explains the study's first author, FLEET Research Fellow Dr Guolin Zheng.

Stronger interlayer coupling in vdW materials would significantly increase potential use in high-temperature devices utilising quantum anomalous Hall effect, and in 2D multiferroics.

The new RMIT-led study demonstrated that coupling in a vdW material, Fe₃GeTe₂ (FGT) nanoflakes, can be largely modulated by a protonic gate.

With the increase of the protons among layers, interlayer magnetic coupling increases.

"Most strikingly, with more protons inserted in FGT nanoflakes at a higher gate voltage, we observed a rarely seen zero-field cooled exchange bias with very large values," says co-author A/Prof Lan Wang.

The successful realization of both field-cooled and zero-field cooled exchange bias in FGT implies the interlayer coupling can be largely modulated by gate-induced proton insertion, opening the road to many applications of vdW materials requiring strong interface coupling.

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Materials provided by ARC Centre of Excellence in Future Low-Energy Electronics Technologies. Note: Content may be edited for style and length.

Journal Reference:

1. Guolin Zheng, Wen-Qiang Xie, Sultan Albarakati, Meri Algarni, Cheng Tan, Yihao Wang, Jingyang Peng, James Partridge, Lawrence Farrar, Jiabao Yi, Yimin Xiong, Mingliang Tian, Yu-Jun Zhao, Lan Wang. Gate-Tuned Interlayer Coupling in van der Waals Ferromagnet Fe3GeTe2 Nanoflakes. Physical Review Letters, 2020; 125 (4) DOI: 10.1103/physrevlett.125.047202