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تسجيل مستخدم جديدScattering-induced and highly tunable by gate damping-like spin-orbit torque in graphene doubly proximitized by two-dimensional magnet Cr$_2$Ge$_2$Te$_6$ and WS$_2$
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Graphene sandwiched between semiconducting monolayers of ferromagnet Cr$_2$Ge$_2$Te$_6$ and transition-metal dichalcogenide WS$_2$ acquires both spin-orbit (SO), of valley-Zeeman and Rashba types, and exchange couplings. Using first-principles combined with quantum transport calculations, we predict that such doubly proximitized graphene within van der Waals heterostructure will exhibit SO torque driven by unpolarized charge current. This system lacking spin Hall current, putatively considered to be necessary for efficient damping-like (DL) SO torque that plays a key role in magnetization switching, demonstrates how DL torque component can be generated solely by skew-scattering off spin-independent potential barrier or impurities in purely two-dimensional electronic transport due to the presence of proximity SO coupling and its spin texture tilted out-of-plane. This leads to current-driven nonequilibrium spin density emerging in all spatial directions, whose cross product with proximity magnetization yields DL SO torque, unlike the ballistic regime with no scatterers in which only field-like (FL) SO torque appears. In contrast to SO torque on conventional metallic ferromagnets in contact with three dimensional SO-coupled materials, the ratio of FL and DL torque can be tuned by more than an order of magnitude via combined top and back gates.
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Electrical control of magnetism of a ferromagnetic semiconductor offers exciting prospects for future spintronic devices for processing and storing information. Here, we report observation of electrically modulated magnetic phase transition and magne
tic anisotropy in thin crystal of Cr$_2$Ge$_2$Te$_6$ (CGT), a layered ferromagnetic semiconductor. We show that heavily electron-doped ($sim$ $10^{14}$ cm$^{-2}$) CGT in an electric double-layer transistor device is found to exhibit hysteresis in magnetoresistance (MR), a clear signature of ferromagnetism, at temperatures up to above 200 K, which is significantly higher than the known Curie temperature of 61 K for an undoped material. Additionally, angle-dependent MR measurements reveal that the magnetic easy axis of this new ground state lies within the layer plane in stark contrast to the case of undoped CGT, whose easy axis points in the out-of-plane direction. We propose that significant doping promotes double-exchange mechanism mediated by free carriers, prevailing over the superexchange mechanism in the insulating state. Our findings highlight that electrostatic gating of this class of materials allows not only charge flow switching but also magnetic phase switching, evidencing their potential for spintronics applications.
Two-dimensional (2D) magnetic materials with strong magnetostriction, like Cr$_2$Ge$_2$Te$_6$ (CGT), provide opportunities for tuning their magnetic state with potential applications in spintronic and magneto-mechanical devices. However, realizing th
is potential requires understanding their mechanical properties, such as the Youngs modulus, and the ability to controllably strain the magnets and monitor their ferromagnetic Curie temperature $T_{rm C}$ on a device level. In this work, we suspend thin CGT layers to form nanomechanical membrane resonators. We then probe the mechanical and magnetic properties of CGT as a function of temperature and strain by static and dynamic nanomechanical methods. Pronounced signatures of magneto-elastic coupling are observed in the temperature-dependent resonance frequency of these membranes at the $T_{rm C}$. We further utilize CGT in heterostructures with thin WSe$_2$ and FePS$_3$ layers to control the strain in CGT flakes and quantitatively probe the transition temperatures of all materials involved. In addition, an enhancement of $T_{rm C}$ by $2.5pm0.6$ K in CGT is realized by electrostatic force straining the heterostructure of $0.016%$ in the absence of an external magnetic field. Nanomechanical strain thus offers a compelling degree of freedom to probe and control magnetic phase transitions in 2D layered ferromagnets and heterostructures.
Spin-orbit coupling in graphene can be increased far beyond its intrinsic value by proximity coupling to a transition metal dichalcogenide. In bilayer graphene, this effect was predicted to depend on the occupancy of both graphene layers, rendering i
t gate-tunable by an out-of-plane electric field. We experimentally confirm this prediction by studying magnetotransport in a dual-gated WSe$_2$/bilayer graphene heterostructure. Weak antilocalization, which is characteristic for phase-coherent transport in diffusive samples with spin-orbit interaction, can be strongly enhanced or suppressed at constant carrier density, depending on the polarity of the electric field. From the spin-orbit scattering times extracted from the fits, we calculate the corresponding Rashba and intrinsic spin-orbit parameters. They show a strong dependence on the transverse electric field, which is well described by a gate-dependent layer polarization of bilayer graphene.
We report the first measurements of spin injection in to graphene through a 20 nm thick tungsten disulphide (WS$_2$) layer, along with a modified spin relaxation time ({tau}s) in graphene in the WS$_2$ environment, via spin-valve and Hanle spin-prece
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