Shiyuan Wang#, Yao Wang#, Shaohua Yan#, Cong Wang#, Bingke Xiang,Keyi Liang,Qiushi He,Kenji Watanabe,Takashi Taniguchi, Shangjie Tian, Hechang Lei, Wei Ji, Yang Qi, Yihua Wang*
Abstract
In two-dimensional (2D) ferromagnets, anisotropy is essential for the magnetic ordering as dictated by the Mermin-Wagner theorem. But when competing anisotropies are present, the phase transition becomes nontrivial. Here, utilizing highly sensitive susceptometry of scanning superconducting quantum interference device microscopy, we probe the spin correlations of ABC-stacked CrBr3 under zero magnetic field. We identify a plateau feature in susceptibility above the critical temperature (�C) in thick samples. It signifies a crossover regime induced by the competition between easy-plane intralayer exchange anisotropy versus uniaxial interlayer anisotropy. The evolution of the critical behavior from the bulk to 2D shows that the competition between the anisotropies is magnified in the reduced dimension. It leads to a strongly frustrated ferromagnetic transition in the bilayer with fluctuation on the order of �C, which is distinct from both the monolayer and the bulk. Our observation demonstrates unconventional 2D critical behavior on a honeycomb lattice.
Mismatched lattice constants at a van der Waals epitaxy interface often introduce in-plane strains to the lattice of the epitaxial layer, termed epitaxy strain, wherein the strains do not follow the intralayer Poisson’s relation. In this study, we obtained the magnetic phase diagrams of CrSe2 and CrTe2 mono- and bilayers under epitaxy strain up to 8%, as predicted using density functional theory calculations. The magnetic phase diagrams indicate that the in-plane epitaxy strain manipulates either the intra- or interlayer magnetism. The in-plane strain varies the interlayer distance, defined using an interlayer Poisson’s ratio, which determines whether the interlayer magnetism follows a Bethe–Slater curve-like (BSC-like) or a reversed BSC-like behavior, depending on the in-plane magnetism. The tunability of the intralayer magnetism is a result of competing intralayer Cr–Cr superexchange interactions. A graphene substrate was introduced to examine the validity of our diagrams in practice. This study also afforded a tentative explanation on the previously reported magnetizations in CrSe2 and CrTe2 epitaxial mono- or bilayers under epitaxy strains, which had given rise to some controversy.
Chen Ye, Cong Wang, Qiong Wu, Sheng Liu, Jiayuan Zhou, Guopeng Wang, Aljoscha Söll, Zdenek Sofer, Ming Yue, Xue Liu, Mingliang Tian, Qihua Xiong, Wei Ji & Xiao Renshaw Wang
Abstract
Magnetic van der Waals (vdW) materials possess versatile spin configurations stabilized in reduced dimensions. One magnetic order is the interlayer antiferromagnetism in A-type vdW antiferromagnet, which may be effectively modified by the magnetic field, stacking order, and thickness scaling. However, atomically revealing the interlayer spin orientation in the vdW antiferromagnet is highly challenging, because most of the material candidates exhibit an insulating ground state or instability in ambient conditions. Here, we report the layer-dependent interlayer antiferromagnetic spin reorientation in air-stable semiconductor CrSBr using magnetotransport characterization and first-principles calculations. We reveal an odd–even layer effect of interlayer spin reorientation, which originates from the competitions among interlayer exchange, magnetic anisotropy energy, and extra Zeeman energy of uncompensated magnetization. Furthermore, we quantitatively constructed the layer-dependent magnetic phase diagram with the help of a linear-chain model. Our work uncovers the layer-dependent interlayer antiferromagnetic spin reorientation engineered by magnetic field in the air-stable semiconductor. (DOI: 10.1021/acsnano.2c01151)
Zijing Zhao, Jian Zhou, Luhao Liu, Nanshu Liu, Jianqi Huang, Biao Zhang, Wei Li, Yi Zeng, Teng Zhang, Wei Ji, Teng Yang, Zhidong Zhang, Songlin Li & Yanglong Hou
Abstract
Two-dimensional (2D) magnetic materials have attracted significant attention for promising applications in energy-saving logic and robust memory devices. However, most 2D magnets discovered so far typically feature drawbacks for practical applications due to low critical temperatures. Herein, we synthesize ultrathin room-temperature (RT) magnetic Fe7Se8 nanoflakes via the space-confined chemical vapor deposition method. It is found that the appropriate supply and control of Se concentration in the reaction chamber is crucial for synthesizing high-quality nonstoichiometric Fe7Se8 nanoflakes. Cryogenic electrical and magnetic characterizations reveal the emergence of spin reorientation at ∼130 K and the survival of long-range magnetic ordering up to room temperature. The RT magnetic domain structures with different thicknesses are also uncovered by magnetic force microscopy. Moreover, theoretical calculations confirm the spin configuration and metallic band structure. The outstanding characteristics exhibited by Fe7Se8 nanoflakes, including RT magnetism, spin reorientation property, and good electrical conductivity, make them a potential candidate for RT spintronics.
Pingfan Gu, Yujia Sun, Cong Wang, Yuxuan Peng, Yaozheng Zhu, Xing Cheng, Kai Yuan, Chao Lyu, Xuelu Liu, Qinghai Tan, Qinghua Zhang, Lin Gu, Zhi Wang, Hanwen Wang, Zheng Han, Kenji Watanabe, Takashi Taniguchi, Jinbo Yang, Jun Zhang, Wei Ji, Ping-Heng Tan & Yu Ye
Abstract
Materials with a quasi-one-dimensional stripy magnetic order often exhibit low crystal and magnetic symmetries, thus allowing the presence of various energy coupling terms and giving rise to macroscopic interplay between spin, charge, and phonon. In this work, we performed optical, electrical and magnetic characterizations combined with first-principles calculations on a van der Waals antiferromagnetic insulator chromium oxychloride (CrOCl). We detected the subtle phase transition behaviors of exfoliated CrOCl under varying temperature and magnetic field and clarified its controversial spin structures. We found that the antiferromagnetism and its air stability persist down to few-layer samples, making it a promising candidate for future 2D spintronic devices. Additionally, we verified the magnetoelastic coupling effect in CrOCl, allowing for the potential manipulation of the magnetic states via electric field or strain. These virtues of CrOCl provide us with an ideal platform for fundamental research on spin-charge, spin-phonon coupling, and spin-interactions.
