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.
Pingfan Gu, Cong Wang, Dan Su, Zehao Dong, Qiuyuan Wang, Zheng Han, Kenji Watanabe, Takashi Taniguchi, Wei Ji, Young Sun & Yu Ye
Abstract:
A promising approach to the next generation of low-power, functional, and energy-efficient electronics relies on novel materials with coupled magnetic and electric degrees of freedom. In particular, stripy antiferromagnets often exhibit broken crystal and magnetic symmetries, which may bring about the magnetoelectric (ME) effect and enable the manipulation of intriguing properties and functionalities by electrical means. The demand for expanding the boundaries of data storage and processing technologies has led to the development of spintronics toward two-dimensional (2D) platforms. This work reports the ME effect in the 2D stripy antiferromagnetic insulator CrOCl down to a single layer. By measuring the tunneling resistance of CrOCl on the parameter space of temperature, magnetic field, and applied voltage, we verified the ME coupling down to the 2D limit and probed its mechanism. Utilizing the multi-stable states and ME coupling at magnetic phase transitions, we realize multi-state data storage in the tunneling devices. Our work not only advances the fundamental understanding of spin-charge coupling, but also demonstrates the great potential of 2D antiferromagnetic materials to deliver devices and circuits beyond the traditional binary operations.
Hanxiang Wu, Jianfeng Guo, Suonan Zhaxi, Hua Xu, Shuo Mi, Le Wang, Shanshan Chen, Rui Xu, Wei Ji, Fei Pang and Zhihai Cheng
Abstract:
As a unique 2D magnetic material with self-intercalated structure, Cr5Te8 exhibits many intriguing magnetic properties. While its ferromagnetism of Cr5Te8 has been previously reported, the research on its magnetic domain remains unexplored. Herein, we have successfully fabricated 2D Cr5Te8 nanosheets with controlled thickness and lateral size by chemical vapor deposition (CVD). Then magnetic property measurement system revealed Cr5Te8 nanosheets exhibiting intense out-of-plane ferromagnetism with a Curie temperature (TC) of 176 K. Significantly, we reported for the first time two magnetic domains: magnetic bubbles and thickness-dependent maze-like magnetic domains in our Cr5Te8 nanosheets by cryogenic magnetic force microscopy (MFM). The domain width of the maze-like magnetic domains increases rapidly with decreasing sample thickness, meanwhile domain contrast decreases. This indicates the dominate role of ferromagnetism shifts from dipolar interactions to magnetic anisotropy. Our research not only establishes a pathway for the controllable growth of 2D magnetic materials, but also points towards novel avenues for regulating magnetic phases and methodically tuning domain characteristics.
Yanyan Geng, Le Lei, Haoyu Dong, Jianfeng Guo, Shuo Mi, Yan Li, Li Huang, Fei Pang, Rui Xu, Weichang Zhou, Zheng Liu, Wei Ji, and Zhihai Cheng
Abstract:
The layered transition metal dichalcogenide 1T−TaS2 has evoked great interest owing to its particularly rich electronic phase diagram including different charge density wave (CDW) phases. However, few studies have focused on its hysteretic electronic phase transitions based on the in-depth discussion of the delicate interplay among temperature-dependent electronic interactions. Here, we report a sequence of spatial electronic phase transitions in the hysteresis temperature range (160–230 K) of 1T−TaS2 via variable-temperature scanning tunneling microscopy. Several emergent electronic states are investigated at multiscale during the commensurate CDW–triclinic CDW (CCDW-TCDW) phase transitions: a spotty-CDW state above ∼160K, a network-CDW (NCDW) state above ∼180K during the warmup process, a belt-TCDW state below ∼230K, a NCDW state below ∼200K, and finally a mosaic-CDW state below ∼160K during cooldown from the TCDW phase. These emergent electronic states are associated with the delicate temperature-dependent competition and/or cooperation of stacking-dependent interlayer interactions, intralayer electron-electron correlations, and electron-phonon (e−ph) coupling of 1T−TaS2. Our results not only provide insight to understand the hysteretic electronic phase transitions in the correlated CDW state, but also pave a way to realize more exotic quantum states by accurately and effectively tuning various interior interactions in correlated materials.
