Giant and Nonvolatile Control of Exchange Bias in Fe₃GeTe₂/Irradiated Fe₃GeTe₂/MgO Heterostructure Through Ultralow Voltage

Abstract

The discovery of van der Waals magnets has provided a new platform for the electrical control of magnetism. Recent experiments have demonstrated that the magnetic properties of van der Waals magnets can be tuned by various gate modulations, although most of them are volatile and require gate voltages no lower than several volts. Here, the realization of nonvolatile control of exchange bias and coercive fields in Fe3GeTe2/MgO heterostructures, and the gate voltage is as low as tens of mV which is two orders of magnitude smaller than those in previous experiments is presented. The discovery of an ionic‐irradiated phase formed in Fe3GeTe2 by MgO sputtering revealed that an exchange bias effect can be obtained in this heterostructure and tuned from ≈700 to 0 Oe through voltages ranging from 5 to 20 mV. Owing to the high stability of oxidized Fe3GeTe2, the voltage‐driven oxygen incorporated into Fe3GeTe2 from the irradiated phase induces a nonvolatile magnetism modulation that can be retained after turning off the gate voltage. These findings demonstrate a methodology to modulate the magnetism of van der Waals magnets, opening new opportunities to fabricate all‐solid, long‐retention, and low‐dissipation nano‐electronic devices using van der Waals materials.

Self-Modulated Magnetism in Two-Dimensional Ferromagnet Fe3GeTe2 Induced by Ambient Effects

“…The above observations for the FGT nanoflake may indicate the coexistence of multiple magnetic phases rather than an individual FM phase, and so the reversal of magnetic moments is not at the same time, which enables the R xy – H curves to form double square-shaped hysteresis loops. Furthermore, the R xy – H curve at 200 K shows an obvious exchange bias effect, as shown in Figure S2, which is similar to the previous literature and indicates multiphase behavior. − We deduce that there are some coupling effects between multiple magnetic phases in oxidized FGT, and coupling strength changes with temperature, resulting in double square-shaped hysteresis loops observed at temperatures above 180 K. When the temperature increases to 210 K, there is no hysteresis loop in the R xy – H curve, showing that the ferromagnetism of the FGT nanoflake disappears above its T C of 200 K.…”

“…The air exposure can effectively promote the formation of multiple magnetic domains in 2D FGT, but not in bulk FGT. 55 The previous literature has shown that O-FGT induced by oxidation of FGT nanoflakes in the ambient environment has antiferromagnetic phases, 51,54,56,57 and a skewed hysteresis loop has also been observed. 58 Moreover, the exchange bias effect has also been observed in oxidized FGT nanoflakes, which demonstrates that antiferromagnetic/ferromagnetic coupling forms at the interface between O-FGT and FGT layers.…”

“…58 Moreover, the exchange bias effect has also been observed in oxidized FGT nanoflakes, which demonstrates that antiferromagnetic/ferromagnetic coupling forms at the interface between O-FGT and FGT layers. 51,53,54 To further elucidate the mechanism of double square-shaped hysteresis loops, a phenomenological model is put forward, as shown in Figure 4. Our model is based on three components of the FGT nanoflake: O-FGT with AFM ordering, severalnanometer scale FGT layers adjacent to O-FGT as FM 1, and internal pure FGT layers as FM 2.…”

“…When sweeping the magnetic field from 3 to −3 kOe, FM 1 and FM 2 show ferromagnetic coupling, and all magnetic moments are saturated and parallel to the external magnetic field at the start (stage i). In this process, interfacial effects are unable to be ignored, especially pinning effects resulting from antiferromagnetic/ferromagnetic coupling between O-FGT and FM 1. ,, The FM 1 layer, that is, several-nanometer scale FGT layers adjacent to the O-FGT, is pinned by antiferromagnetic/ferromagnetic coupling at the interface, so that magnetic moments of FM 1 are more difficult to be reversed by an external magnetic field and magnetic moments of FM 2 reverse first (stage ii). In Figure a, Hall resistance R xy decreases sharply for the first time at a low negative magnetic field, which indicates that the magnetic properties of FM 2 are similar to well-preserved FGT.…”

Electric control of optically-induced magnetization dynamics in a van der Waals ferromagnetic semiconductor

“…Most works on the electric control of magnetization in vdW magnets have focused on their magnetostatic properties, such as the magnetic anisotropy, saturation magnetization and Curie temperature, in both metallic 32 – 35 and semiconducting 21 – 25 materials. In contrast, their magnetization dynamics have only recently started to receive more attention, and have been studied using microwave-driven magnetic resonance 36 – 43 , or time-dependent magneto-optic techniques 44 – 52 .…”