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Register a new userMagnetic Proximity Effect in 2D Ferromagnetic CrBr3/Graphene van der Waals Heterostructures
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Two-dimensional (2D) van der Waals heterostructures serve as a promising platform to exploit various physical phenomena in a diverse range of novel spintronic device applications. The efficient spin injection is the prerequisite for these devices. The recent discovery of magnetic 2D materials leads to the possibility of fully 2D van der Waals spintronics devices by implementing spin injection through magnetic proximity effect (MPE). Here, we report the investigation of magnetic proximity effect in 2D CrBr3/graphene van der Waals heterostructures, which is probed by Zeeman spin Hall effect through non-local measurements. Zeeman splitting field estimation demonstrates a significant magnetic proximity exchange field even in a low magnetic field. Furthermore, the observed anomalous longitudinal resistance changes at the Dirac point R_(XX,D)with increasing magnetic field at { u} = 0 may attribute to the MPE induced new ground state phases. This MPE revealed in our CrBr3/graphene van der Waals heterostructures therefore provides a solid physics basis and key functionality for next generation 2D spin logic and memory devices.
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We report on first-principle calculations on magnetic proximity effect in a van der Waals heterostructure formed by a graphene monolayer induced by its interaction with a two-dimensional (2D) ferromagnet (chromium tribromide, CrBr3). We observe that the magnetic proximity effect arising from the spin-dependent interlayer coupling depends sensitively on the interlayer electronic configuration. The proximity effect results in spin polarization of graphene orbital by up to 63.6 %, together with a miniband splitting band gap of about 73.4 meV and 8% enhancement in magnetic moment (3.47${mu}$B/cell) in heterostructure. The position of the Fermi level in the Dirac cone is shown to depend strongly on the graphene-CrBr3 interlayer separation of 3.77 Angstrom. Consequently, we also show that a perpendicular electric field can be used to control the miniband spin splitting and transmission spectrum. Also, the interfacial polarization effect due to the existence of two different constituents reinforces the conductivity via electrostatic screening in the heterolayer. These findings point toward potential nanoscale devices where the electric field driven magnetic proximity effect can lead to unique spin controllability and possible engineering of spin gating.
Magnetic proximity effects are crucial ingredients for engineering spintronic, superconducting, and topological phenomena in heterostructures. Such effects are highly sensitive to the interfacial electronic properties, such as electron wave function overlap and band alignment. The recent emergence of van der Waals (vdW) magnets enables the possibility of tuning proximity effects via designing heterostructures with atomically clean interfaces. In particular, atomically thin CrI3 exhibits layered antiferromagnetism, where adjacent ferromagnetic monolayers are antiferromagnetically coupled. Exploiting this magnetic structure, we uncovered a layer-resolved magnetic proximity effect in heterostructures formed by monolayer WSe2 and bi/trilayer CrI3. By controlling the individual layer magnetization in CrI3 with a magnetic field, we found that the spin-dependent charge transfer between WSe2 and CrI3 is dominated by the interfacial CrI3 layer, while the proximity exchange field is highly sensitive to the layered magnetic structure as a whole. These properties enabled us to use monolayer WSe2 as a spatially sensitive magnetic sensor to map out layered antiferromagnetic domain structures at zero magnetic field as well as antiferromagnetic/ferromagnetic domains near the spin-flip transition in bilayer CrI3. Our work reveals a new way to control proximity effects and probe interfacial magnetic order via vdW engineering.
The development of van der Waals (vdW) crystals and their heterostructures has created a fascinating platform for exploring optoelectronic properties in the two-dimensional (2D) limit. With the recent discovery of 2D magnets, the control of the spin degree of freedom can be integrated to realize 2D spin-optoelectronics with spontaneous time-reversal symmetry breaking. Here, we report spin photovoltaic effects in vdW heterostructures of atomically thin magnet chromium triiodide (CrI3) sandwiched by graphene contacts. In the absence of a magnetic field, the photocurrent displays a distinct dependence on light helicity, which can be tuned by varying the magnetic states and photon energy. Circular polarization-resolved absorption measurements reveal that these observations originate from magnetic-order-coupled and thus helicity-dependent charge-transfer exciton states. The photocurrent displays multiple plateaus as the magnetic field is swept, which are associated with different spin configurations enabled by the layered antiferromagnetism and spin-flip transitions in CrI3. Remarkably, giant photo-magnetocurrent is observed, which tends to infinity for a small applied bias. Our results pave the way to explore emergent photo-spintronics by engineering magnetic vdW heterostructures.
Graphene constitutes one of the key elements in many functional van der Waals heterostructures. However, it has negligible optical visibility due to its monolayer nature. Here we study the visibility of graphene in various van der Waals heterostructures and include the effects of the source spectrum, oblique incidence and the spectral sensitivity of the detector to obtain a realistic model. A visibility experiment is performed at different wavelengths, resulting in a very good agreement with our calculations. This allows us to reliably predict the conditions for better visibility of graphene in van der Waals heterostructures. The framework and the codes provided in this work can be extended to study the visibility of any 2D material within an arbitrary van der Waals heterostructure.
The Raman 2D line of graphene is widely used for device characterization and during device fabrication as it contains valuable information on e.g. the direction and magnitude of mechanical strain and doping. Here we present systematic asymmetries in the 2D line shape of exfoliated graphene and graphene grown by chemical vapor deposition. Both graphene crystals are fully encapsulated in van der Waals heterostructures, where hexagonal boron nitride and tungsten diselenide are used as substrate materials. In both material stacks, we find very low doping values and extremely homogeneous strain distributions in the graphene crystal, which is a hall mark of the outstanding electronic quality of these samples. By fitting double Lorentzian functions to the spectra to account for the contributions of inner and outer processes to the 2D peak, we find that the splitting of the sub-peaks, $6.6 pm 0.5$ cm$^{-1}$(hBN-Gr-WSe2) and $8.9 pm 1.0$ cm$^{-1}$ (hBN-Gr-hBN), is significantly lower than the values reported in previous studies on suspended graphene.
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