Magnetoelectric Response of Antiferromagnetic CrI3 Bilayers (original) (raw)
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High-Curie-temperature ferromagnetism in bilayer CrI3 on bulk semiconducting substrates
Physical Review Materials
Two-dimensional (2D) ferromagnetic (FM) semiconductors with high Curie temperature have long been pursued for electronic and spintronic applications. Here we provide a general strategy to achieve robust FM state in bilayer CrI 3 of the monoclinic stacking, which intrinsically has interlayer antiferromagnetic (AFM) order and weak in-plane FM coupling. We showed that the proximity effect from bulk semiconducting substrates induces electronic doping and significantly increases the FM nearest-neighbor exchange for bilayer CrI 3 , leading to the AFM-to-FM transition for the interlayer spin configuration as well as enhanced intralayer FM coupling. By first-principles calculations and Monte Carlo simulations, bulk and 2D semiconductors providing different interaction strengths from strong covalent bonding to weak van der Waals (vdW) interaction with CrI 3 are compared to thoroughly address the substrate effect on magnetic behavior and Curie temperature of bilayer CrI 3. These theoretical results offer a facile route for direct synthesis of 2D ferromagnets on proper semiconducting substrates to achieve high Curie temperature for device implementation.
Advanced Materials, 2020
The recent discovery of magnetism within the family of exfoliatable van der Waals (vdW) compounds has attracted considerable interest in these materials for both fundamental research and technological applications. However current vdW magnets are limited by their extreme sensitivity to air, low ordering temperatures, and poor charge transport properties. Here we report the magnetic and electronic properties of CrSBr, an air-stable vdW antiferromagnetic semiconductor that readily cleaves perpendicular to the stacking axis. Below its Néel temperature, T N = 132 ± 1 K, CrSBr adopts an A-type antiferromagnetic structure with each individual layer ferromagnetically ordered internally and the layers coupled antiferromagnetically along the stacking direction. Scanning tunneling spectroscopy and photoluminescence (PL) reveal that the electronic gap is Δ E = 1.5 ± 0.2 eV with a corresponding PL peak centered at 1.25 ± 0.07 eV. Using magnetotransport measurements, we demonstrate strong coupling between magnetic order and transport properties in CrSBr, leading to a large negative magnetoresistance response that is unique amongst vdW materials. These findings establish CrSBr as a promising material platform for increasing the applicability of vdW magnets to the field of spin-based electronics. Main Text: Materials that combine bulk magnetic order and semiconducting transport properties have received widespread attention for their ability to control both charge and spin carriers, allowing for complete spin polarization of their conduction electrons. [1] By exploiting the spins of electrons as information carriers, instead of their charge, these materials promise to improve the speed, density, and energy efficiency of electronic devices through single-spin transport. [2-4] This makes magnetic semiconductors particularly attractive for device applications that utilize the electronic tunability, spin-polarized transport, and exotic magneto-optical properties characteristic of magnetic
Electronic correlation, magnetic structure, and magnetotransport in few-layer CrI3
Physical Review Materials, 2020
Using density functional theory combined with a Hubbard model (DFT+U), the electronic band structure of CrI3 multilayers, both free-standing and enclosed between graphene contacts, is calculated. We show that the DFT+U approach, together with the 'around mean field' correction scheme, is able to describe the vertical magnetotransport in line with the experimental measurements of magnetoresistance in multi-layered CrI3 enclosed between graphene contacts. Moreover, by interpolating between different double-counting correction schemes, namely the 'around mean field' correction and the fully localized limit, we show their importance for describing both the band structure and the ground-state total energy consistently. Our description of the magnetic exchange interaction is compatible with the experimentally observed antiferromagnetic ground state in the bilayer CrI3 and the transition to a ferromagnetic arrangement in a small external magnetic field. Thus, using spin-polarized DFT+U with an 'around mean field' correction, a consistent overall picture is achieved.
Coupling of Crystal Structure and Magnetism in the Layered, Ferromagnetic Insulator CrI3
Chemistry of Materials, 2015
We have examined the crystallographic and magnetic properties of single crystals of CrI 3 , an easily cleavable, layered and insulating ferromagnet with a Curie temperature of 61 K. Our X-ray diffraction studies reveal a first-order crystallographic phase transition occurring near 210−220 K upon warming, with significant thermal hysteresis. The low-temperature structure is rhombohedral (R3̅ , BiI 3type) and the high-temperature structure is monoclinic (C2/ m, AlCl 3-type). We find evidence for coupling between the crystallographic and magnetic degrees of freedom in CrI 3 , observing an anomaly in the interlayer spacing at the Curie temperature and an anomaly in the magnetic susceptibility at the structural transition. First-principles calculations reveal the importance of proper treatment of the long-ranged interlayer forces, and van der Waals density functional theory does an excellent job of predicting the crystal structures and their relative stability. Calculations also suggest that the ferromagnetic order found in the bulk material may persist into monolayer form, suggesting that CrI 3 and other chromium trihalides may be promising materials for spintronic and magnetoelectronic research.
Electric-field control of magnetism in a few-layered van der Waals ferromagnetic semiconductor
Nature nanotechnology, 2018
Manipulating a quantum state via electrostatic gating has been of great importance for many model systems in nanoelectronics. Until now, however, controlling the electron spins or, more specifically, the magnetism of a system by electric-field tuning has proven challenging. Recently, atomically thin magnetic semiconductors have attracted significant attention due to their emerging new physical phenomena. However, many issues are yet to be resolved to convincingly demonstrate gate-controllable magnetism in these two-dimensional materials. Here, we show that, via electrostatic gating, a strong field effect can be observed in devices based on few-layered ferromagnetic semiconducting CrGeTe. At different gate doping, micro-area Kerr measurements in the studied devices demonstrate bipolar tunable magnetization loops below the Curie temperature, which is tentatively attributed to the moment rebalance in the spin-polarized band structure. Our findings of electric-field-controlled magnetism...
Journal of Chemical Physics, 2022
The first magnetic 2D material discovered, monolayer (ML) CrI 3 , is particularly fascinating due to its ground state ferromagnetism. Yet, because monolayer materials are difficult to probe experimentally, much remains unresolved about ML CrI 3 's structural, electronic, and magnetic properties. Here, we leverage Density Functional Theory (DFT) and high-accuracy Diffusion Monte Carlo (DMC) simulations to predict lattice parameters, magnetic moments, and spin-phonon and spin-lattice coupling of ML CrI 3. We exploit a recently developed surrogate Hessian DMC line search technique to determine CrI 3 's monolayer geometry with DMC accuracy, yielding lattice parameters in good agreement with recently-published STM measurements-an accomplishment given the ∼ 10% variability in previous DFT-derived estimates depending upon the functional. Strikingly, we find previous DFT predictions of ML CrI 3 's magnetic spin moments are correct on average across a unit cell, but miss critical local spatial fluctuations in the spin density revealed by more accurate DMC. DMC predicts magnetic moments in ML CrI 3 are 3.62 µ B per chromium and-0.145 µ B per iodine; both larger than previous DFT predictions. The large disparate moments together with the large spin-orbit coupling of CrI 3 's I-p orbital suggests a ligand superexchange-dominated magnetic anisotropy in ML CrI 3 , corroborating recent observations of magnons in its 2D limit. We also find ML CrI 3 exhibits a substantial spin-phonon coupling of ∼ 3.32 cm −1. Our work thus establishes many of ML CrI 3 's key properties, while also continuing to demonstrate the pivotal role DMC can assume in the study of magnetic and other 2D materials.
Magnetic exchange interactions in monolayer CrI3 from many-body wavefunction calculations
2D Materials, 2020
The marked interplay between the crystalline, electronic, and magnetic structure of atomically thin magnets has been regarded as the key feature for designing next-generation magneto-optoelectronic devices. In this respect, a detailed understanding of the microscopic interactions underlying the magnetic response of these crystals is of primary importance. Here, we combine model Hamiltonians with multireference configuration interaction wavefunctions to accurately determine the strength of the spin couplings in the prototypical single-layer magnet CrI3. Our calculations identify the (ferromagnetic) Heisenberg exchange interaction J = −1.44 meV as the dominant term, being the inter-site magnetic anisotropies substantially weaker. We also find that single-layer CrI3 features an out-of-plane easy axis ensuing from a single-ion anisotropy A = −0.10 meV, and predict g-tensor in-plane components g x x = g y y = 1.90 and out-of-plane component g zz = 1.92. In addition, we assess the perfor...
Magnetism and magneto-optical effects in bulk and few-layer CrI3: a theoretical GGA + U study
New Journal of Physics, 2019
The latest discovery of ferromagnetism in atomically thin films of semiconductors Cr2Ge2Te6 and CrI3 has unleashed numerous opportunities for fundamental physics of magnetism in two-dimensional (2D) limit and also for technological applications based on 2D magnetic materials. To exploit these 2D magnetic materials, however, the mechanisms that control their physical properties should be thoroughly understood. In this paper, we present a comprehensive theoretical study of the magnetic, electronic, optical and magneto-optical (MO) properties of multilayers (monolayer (ML), bilayer (BL) and trilayer) as well as bulk CrI3, based on the density functional theory with the generalized gradient approximation plus on-site Coulomb repulsion scheme. Interestingly, all the structures except the BL, are found to be single-spin ferromagnetic semiconductors. They all have a large out-of-plane magnetic anisotropy energy (MAE) of ∼0.5 meV/Cr, in contrast to the significantly thickness-dependent MAE ...
Atomically Thin CrCl3: An In-Plane Layered Antiferromagnetic Insulator
Nano Letters
The recent discovery of magnetism in atomically thin layers of van der Waals (vdW) crystals has created new opportunities for exploring magnetic phenomena in the twodimensional (2D) limit. In most 2D magnets studied to date the c-axis is an easy axis, so that at zero applied field the polarization of each layer is perpendicular to the plane. Here, we demonstrate that atomically thin CrCl3 is a layered antiferromagnetic insulator with an easyplane normal to the c-axis, that is the polarization is in the plane of each layer and has no preferred direction within it. Ligand field photoluminescence at 870 nm is observed down to the monolayer limit, demonstrating its insulating properties. We investigate the in-plane magnetic order using tunneling magnetoresistance in graphene/CrCl3/graphene tunnel junctions, establishing that the interlayer coupling is antiferromagnetic down to the bilayer. From the temperature dependence of the magnetoresistance we obtain an effective magnetic phase diagram for the bilayer. Our result shows that CrCl3 should be useful for studying the physics of 2D phase transitions and for making new kinds of vdW spintronic devices.
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Nature nanotechnology, 2018
Controlling magnetism via electric fields addresses fundamental questions of magnetic phenomena and phase transitions, and enables the development of electrically coupled spintronic devices, such as voltage-controlled magnetic memories with low operation energy. Previous studies on dilute magnetic semiconductors such as (Ga,Mn)As and (In,Mn)Sb have demonstrated large modulations of the Curie temperatures and coercive fields by altering the magnetic anisotropy and exchange interaction. Owing to their unique magnetic properties, the recently reported two-dimensional magnets provide a new system for studying these features. For instance, a bilayer of chromium triiodide (CrI) behaves as a layered antiferromagnet with a magnetic field-driven metamagnetic transition. Here, we demonstrate electrostatic gate control of magnetism in CrI bilayers, probed by magneto-optical Kerr effect (MOKE) microscopy. At fixed magnetic fields near the metamagnetic transition, we realize voltage-controlled s...