Electrically Controlled Exchange-bias Effect Discovered in Magnetic Van Der Waals Heterostructures

Van der Waals (vdW) ferromagnets are the building blocks of vdW heterostructure devices such as vdW ferromagnetic (FM)-antiferromagnetic (AFM) heterostructure, vdW FM-ferroelectric heterostructure. Those vdW heterostructure devices have attracted a lot of attention due to their promising applications in modern spintronics. However, the interface coupling of vdW heterostructure is weak due to the large vdW gap, which impedes the development of this burgeoning area. How to electrically tune the interface coupling in vdW heterostructure device remains elusive.

Recently, professor ZHENG Guolin from High Magnetic field laboratory, Hefei Institutes of Physical Science of Chinese Academy of Sciences (CAS), collaborated with professor Lan Wang from Royal Melbourne Institute of Technology University, experimentally studied the interface coupling in FePS₃-Fe₅GeTe₂ van der Waals heterostructures via proton intercalations.

This is the first time scientists discovered that the interface coupling induced exchange bias effect can be electrically controlled via gate-induced proton intercalations, which provided a promising way to manipulate the interface coupling in many more vdW heterostructures.

The research result was recently published in Nano Letters.

In this research, the team fabricated FePS₃-Fe₅GeTe₂ vdW heterostructure devices (with the thickness of FM layer Fe₅GeTe₂ between 12-18 nm) and showed that the weak exchange bias effects below 20 K developed due to the interface magnetic coupling.

However, when they put the heterostructure devices onto the solid proton conductors, the blocking temperature (where the exchange bias effect disappeared) was largely boosted up to 60 K. Moreover, the observed exchange bias effect can be electrically switched “ON” and “OFF” due to the intercalations or de-intercalations of the protons under a gate voltage.

Interestingly, the magnetic properties of the top Fe₃GeTe₂ layer including coercivity, anomalous Hall resistivity and Curie temperature didn’t change during the whole gating process, revealing that the proton intercalation has a very limited impact on FM layer.

Further theoretical calculations based on density functional theory demonstrated that the proton intercalations mainly affected the magnetic coupling at the interface as well as the magnetic configurations in AFM layer, leading to a gate-tunable exchange bias effect.

This work was financially supported by the Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies, the National Natural Science Foundation of China and the Key Research and Development Project of Guangdong Province.

(a) Schematic of the solid proton field effect transistor. (b, c) Optical and atomic force microscope images of heterostructure device. (d, e) Gate-dependent exchange bias effects at T = 30 and 40 K, respectively. (f, g) Amplitudes of the exchange bias effects under various gating voltages at T = 30 and 40 K, respectively. (Image by ZHENG Guolin)