Miniaturizing van der Waals (vdW) ferroelectric materials to atomic scales is essential for modern devices like nonvolatile memory and sensors. To unlock their full potential, their growth mechanisms, interface effects, and stabilization are preferably investigated, particularly for ultrathin 2D nanosheets with single-unit cell thickness. This study focuses on Bi2TeO5 (BTO) and utilizes precise control over growth kinetics at the nucleation temperature to create specific interfacial reconfiguration layers. Ultrathin BTO nanosheets with planar ferroelectricity at a single-unit cell thickness are successfully grown. Atomic-scale characterization reveals a disordered distribution of elements in the interfacial layer, which buffers strain from lattice mismatch. The theoretical calculations support these observations. Furthermore, this strategy also can be extended to the growth of a variety of 2D ternary oxide nanosheets. This work contributes to a better understanding of growth and stability mechanisms in 2D ultrathin nanosheets.
Charge carrier densities in electronic heterostructures are typically responsive to external electric fields or chemical doping but rarely to their magnetization history. Here, we demonstrate that magnetization acts as a non-volatile control parameter for the density of states in bilayer graphene (BLG) interfaced with the antiferromagnetic insulator chromium oxychloride (COC). Using capacitance measurements, we observe a hysteretic behavior in the density of states of BLG on a COC substrate in response to an external magnetic field, which is unrelated to the history of electrostatic gating. First-principles calculations revealed that such hysteresis arises from the magnetic-field-controlled charge transfer between BLG and COC during the antiferromagnetic (AFM) to ferrimagnetic-like (FiM) state phase transition of COC. Our work demonstrates that interfacial charging states can be effectively controlled magnetically, and it also shows that capacitance measurement is a suitable technique for detecting subtle changes not detectable via conventional resistivity measurements. These findings broaden the scope of proximity effects and open new possibilities for nanoelectronics applications.
The quest for pragmatic room-temperature (RT) magnetic semiconductors (MSs) with a suitable bandgap constitutes one of the contemporary opportunities to be exploited. This may provide a materials platform for to bring new-generation ideal information device technologies into real-world applications where the otherwise conventionally separately utilized charge and spin are simultaneously exploited. Here we present RT ferromagnetism in an Fe-doped SnSe (Fe:SnSe) van der Waals (vdW) single crystalline ferromagnetic semiconductor (FMS) with a semiconducting bandgap of ∼1.19 eV (comparable to those of Si and GaAs). The synthesized Fe:SnSe single crystals feature a dilute Fe content of <1.0 at%, a Curie temperature of ∼310 K, a layered vdW structure nearly identical to that of pristine SnSe, and the absence of in-gap defect states. The Fe:SnSe vdW diluted magnetic semiconductor (DMS) single crystals are grown using a simple temperature-gradient melt-growth process, in which the magnetic Fe atom doping is realized uniquely using FeI2 as the dopant precursor whose melting point is low with respect to crystal growth, and which in principle possesses industrially unlimited scalability. Our work adds a new member in the family of long-searching RT magnetic semiconductors, and may establish a generalized strategy for large-volume production of related DMSs.
Yueshen Wu, Yuxiong Hu, Cong Wang, Xiang Zhou, Xiaofei Hou, Wei Xia, Yiwen Zhang, Jinghui Wang, Yifan Ding, Jiadian He, Peng Dong, Song Bao, Jinsheng Wen, Yanfeng Guo, Kenji Watanabe, Takashi Taniguchi, Wei Ji, Zhu-Jun Wang, Jun Li
Abstract:
Fe3GeTe2 have proven to be of greatly intrigue. However, the underlying mechanism behind the varying Curie temperature (Tc) values remains a puzzle. Here, we explored the atomic structure of Fe3GeTe2 crystals exhibiting Tc values of 160, 210, and 230 K. The elemental mapping reveals a Fe-intercalation on the interstitial sites within the van der Waals gap of the high- Tc (210 and 230 K) samples, which are observed an exchange bias effect by electrical transport measurements, while Fe intercalation or the bias effect is absent in the low-Tc (160 K) samples. First-principles calculations further suggest that the Fe-intercalation layer may be responsible for the local antiferromagnetic coupling that gives rise to the exchange bias effect, and that the interlayer exchange paths greatly contributes to the enhancement of Tc. This discovery of the Fe-intercalation layer elucidates the mechanism behind the hidden antiferromagnetic ordering that underlies the enhancement of Tc in Fe3GeTe2.
