Evolution of interlayer and intralayer magnetism in three atomically thin chromium trihalides
Hyun Ho Kim, Bowen Yang, Siwen Li, Shengwei Jiang, Chenhao Jin, Zui Tao, George Nichols, Francois Sfigakis, Shazhou Zhong, Chenghe Li, Shangjie Tian, David G. C… 展开作者
Hyun Ho Kim, Bowen Yang, Siwen Li, Shengwei Jiang, Chenhao Jin, Zui Tao, George Nichols, Francois Sfigakis, Shazhou Zhong, Chenghe Li, Shangjie Tian, David G. Cory, Guo-Xing Miao, Jie Shan, Kin Fai Mak, Hechang Lei, Kai Sun, Liuyan Zhao, Adam W. Tsen
We conduct a comprehensive study of three different magnetic semiconductors, CrI$_3$, CrBr$_3$, and CrCl$_3$, by incorporating both few- and bi-layer samples in van der Waals tunnel junctions. We find that the interlayer magnetic ordering, exchange gap, magnetic anisotropy, as well as magnon excitations evolve systematically with changing halogen atom. By fitting to a spin wave theory that accounts for nearest neighbor exchange interactions, we are able to further determine a simple spin Hamiltonian describing all three systems. These results extend the 2D magnetism platform to Ising, Heisenberg, and XY spin classes in a single material family. Using magneto-optical measurements, we additionally demonstrate that ferromagnetism can be stabilized down to monolayer in more isotropic CrBr$_3$, with transition temperature still close to that of the bulk.
Chromium trihalides (CrI$_3$, CrBr$_3$ and CrCl$_3$) form a prominent family of isostructural insulating layered materials in which ferromagnetic order has been observed down to the monolayer. Here we provide a comprehensive computational study of magneto-optical properties that are used as probes for the monolayer ferromagnetic order: magnetic circular dichroism and magneto-optic Kerr effect. Using a combination of density functional and Bethe-Salpeter theories, we calculate both the optical absorption and the magneto-optical Kerr angle spectra, including both excitonic effects and spinorial …
Materials that demonstrate large magnetoresistance have attracted significant interest for many decades. Recently, extremely large tunnel magnetoresistance (TMR) has been reported by several groups across ultrathin CrI$_3$ by exploiting the weak antiferromagnetic coupling between adjacent layers. Here, we report a comparative study of TMR in all three chromium trihalides (CrX$_3$, X= Cl, Br, or I) in the two-dimensional limit. As the materials exhibit different transition temperatures and interlayer magnetic ordering in the ground state, tunneling measurements allow for an easy determination o…
Chromium trihalides, CrX$_3$ (with X = Cl, Br, I), are a family of layered magnetic materials that can be easily exfoliated to provide ferromagnetic monolayers. When two layers are stacked together to form a bilayer the interlayer exchange coupling can be either ferromagnetic or antiferromagnetic depending on the stacking sequence. Here we combine crystallographic arguments based on the close-packing condition with first-principles simulations to enumerate all possible stacking patterns in CrX$_3$ bilayers that preserve the spatial periodicity of each layer. We recover all configurations obser…
Magnetic skyrmions are nano-scale spin structures that are promising for ultra-dense memory and logic devices. Recent progresses in two-dimensional magnets encourage the idea to realize skyrmionic states in freestanding monolayers. However, monolayers such as CrI3 lack Dzyaloshinskii-Moriya interactions (DMI) and thus do not naturally exhibit skyrmions but rather a ferromagnetic state. Here we propose the fabrication of Cr(I,X)3 Janus monolayers, in which the Cr atoms are covalently bonded to the underlying I ions and top-layer Br or Cl atoms. By performing first-principles calculations and Mo…
Understanding the coupling between spin and phonons is critical for controlling the lattice thermal conductivity ($κ_l$) in magnetic materials, as we demonstrate here for CrX$_3$ (X = Br and I) monolayers. We show that these compounds exhibit large spin-phonon coupling (SPC), dominated by out-of-plane vibrations of Cr atoms, resulting in significantly different phonon dispersions in ferromagnetic (FM) and paramagnetic (PM) phases. Lattice thermal conductivity calculations provide additional evidence for strong SPC, where particularly large $κ_l$ is found for the FM phase. Most strikingly, PM a…
Monolayer chromium trihalides, the archetypal two dimensional (2D) magnetic materials, are readily suggested as a promising platform for high frequency magnonics. Here we detail the spin wave properties of monolayer CrBr$_3$ and CrI$_3$, using spin dynamics simulations parametrized from the first principles. We reveal that spin wave dispersion can be tuned in a broad range of frequencies by strain, paving the way towards flexo magnonic applications. We further show that ever present halide vacancies in these monolayers host sufficiently strong Dzyaloshinskii Moriya interaction to scatter spin …
The mechanical properties of magnetic materials are instrumental for the development of the magnetoelastic theory and the optimization of strain-modulated magnetic devices. In particular, two-dimensional (2D) magnets hold promise to enlarge these concepts into the realm of low-dimensional physics and ultrathin devices. However, no experimental study on the intrinsic mechanical properties of the archetypal 2D magnet family of the chromium trihalides has thus far been performed. Here, we report the room temperature layer-dependent mechanical properties of atomically thin CrI3 and CrCl3, finding …
Alloy engineering of Magnetic phases in two-dimensional Chromium Trihalides
Institute of Physics, University of São Paulo（圣保罗大学物理研究所）；Department of Theoretical and Computational Chemistry, National University of Córdoba（科尔多瓦国立大学理论与计算化学系）；Department of Materials Engineering, University of São Paulo（圣保罗大学材料工程系）
A contrastive investigation of the symmetry aspects of phonons in monolayer chromium trihalides and their Janus structures Y$_3$-Cr$_2$-X$_3$ (X, Y = F, Cl, Br, I) by group theory is presented. We first classify all phonons at the Brillouin-zone center ($Γ$) into the irreducible representation. Then the infrared and Raman activity of optic phonons, Raman tensors, and the possible polarization assignments of R active phonons are predicted. Base on these results, we clarify the the discrepancy about the Raman activity o optic modes in monolayer CrI$_3$. Besides, we find that the Raman and infrar…
Two-dimensional (2D) intrinsic ferromagnetic (FM) semiconductors are crucial to develop low-dimensional spintronic devices. Using density functional theory, we show that single-layer chromium trihalides (SLCTs) (CrX$_3$,X=F, Cl, Br and I) constitute a series of stable 2D intrinsic FM semiconductors. A free-standing SLCT can be easily exfoliated from the bulk crystal, due to a low cleavage energy and a high in-plane stiffness. Electronic structure calculations using the HSE06 functional indicate that both bulk and single-layer CrX$_3$ are half semiconductors with indirect gaps and their valence…
Most transition-metal trihalides are dimorphic. The representative chromium-based triad, CrCl3, CrBr3, CrI3, is characterized by the low-temperature phase adopting the trigonal BiI3 type while the structure of the high-temperature phase is monoclinic of AlCl3 type (C2/m). The structural transition between the two crystallographic phases is of the first-order type with large thermal hysteresis in CrCl3 and CrI3. We studied crystal structures and structural phase transitions of vanadium-based counterparts VCl3, VBr3, and VI3 by measuring specific heat, magnetization, and X-ray diffraction as fun…
Recently the discovery of magnetic order in two-dimensional monolayer chromium trihalides opens the new research field in two-dimensional materials. We use first-principles calculations to systematically examine the doping effect of chalcogen on CrBr3. In the case of S-doping, four stable configurations, Cr2Br5S, Cr2Br4S2-A, Cr2Br4S2-B and Cr2Br3S3-A, are predicted to be ferromagnetic semiconductors. It is found that the new bands appearing in the original bandgap are made up of S-p and Cr-d-egorbits, lead to the obvious reduce of bandgap and the enhanced optical absorption in the visible rang…
Van der Waals (VdW) materials have opened new directions in the study of low dimensional magnetism. A largely unexplored arena is the intrinsic tuning of VdW magnets toward new ground-states. The chromium trihalides provided the first such example with a change of inter-layer magnetic coupling emerging upon exfoliation. Here, we take a different approach to engineer new ground-states, not by exfoliation, but by tuning the spin-orbit coupling (SOC) of the non-magnetic ligand atoms (Cl,Br,I). We synthesize a three-halide series, CrCl$_{3-x-y}$Br$_{x}$I$_{y}$, and map their magnetic properties as…
We calculate the Curie temperature of layered ferromagnets, chromium tri-iodide (CrI3), chromium tri-bromide (CrBr3), chromium germanium tri-telluride (CrGeTe3), and the Neel temperature of a layered anti-ferromagnet iron di-chloride (FeCl2), using first-principles density functional theory calculations and Monte-Carlo simulations. We develop a computational method to model the magnetic interactions in layered magnetic materials and calculate their critical temperature. We provide a unified method to obtain the magnetic exchange parameters (J) for an effective Heisenberg Hamiltonian from first…
Activated Migration of Localized Ligand-Field Excitons in Atomically Thin CrCl3
Pohang University of Science and Technology (POSTECH)（浦项科技大学）；Sungkyunkwan University（成均馆大学）；National Institute for Materials Science（国立材料研究所）；Institute for Basic Science (IBS)（基础科学研究院）
Exfoliated chromium triiodide (CrI$_3$) is a layered van der Waals (vdW) magnetic insulator that consists of ferromagnetic layers coupled through antiferromagnetic interlayer exchange. The resulting permutations of magnetic configurations combined with the underlying crystal symmetry produces tunable magneto-optical phenomena that is unique to the two-dimensional (2D) limit. Here, we report the direct observation of 2D magnons through magneto-Raman spectroscopy with optical selection rules that are strictly determined by the honeycomb lattice and magnetic states of atomically thin CrI$_3$. In …
