Controlling Magnetic and Optical Properties of the van der Waals Crystal CrCl3−xBrx via Mixed Halide Chemistry

Abramchuk, Mykola; Jaszewski, Samantha T.; Metz, Kenneth R.; Osterhoudt, Gavin B.; Wang, Yiping; Burch, Kenneth S.; Tafti, Fazel

doi:10.1002/adma.201801325

Cited by 120 publications

(71 citation statements)

References 30 publications

(50 reference statements)

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“…One can see that the heavier the halide, the stronger the tendency to the out-of-plane orientation of the moments. This fact has also been observed experimentally for the series of Cr(Cl x , Br 1−x ) 3 compounds [82]. Prior DFT calculations, based on VASP, predicted the monolayer of CrCI 3 to have weak out-of-plane anisotropy [42,81].…”

Section: B 2d Periodic Monolayerssupporting

confidence: 67%

Relativistic exchange interactions in CrX3 ( X=Cl , Br, I) monolayers

et al. 2020

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It has been predicted theoretically and indirectly confirmed experimentally that single-layer CrX 3 (X = Cl, Br, I) might be the prototypes of topological magnetic insulators (TMI). In this work, by using first-principles calculations combined with atomistic spin dynamics, we provide a complete picture of the magnetic interactions and magnetic excitations in CrX 3. The focus is here on the two most important aspects for the actual realization of TMI, namely the relativistic magnetic interactions and the finite-size (edge) effects. We compute the full interaction tensor, which includes both Kitaev and Dzyaloshinskii-Moriya (DM) terms, which are considered as the most likely mechanisms for stabilizing topological magnons. First, we instigate the properties of bulk CrI 3 and compare the simulated magnon spectrum with the experimental data [Phys. Rev. X 8, 041028 (2018)]. Our results suggest that a large size of topological gap, seen in experiment (≈4 meV), cannot be explained by considering pair-wise spin interactions only. We identify several possible reasons for this disagreement. The magnetic interactions in the monolayers of CrX 3 are also investigated. The strength of the anisotropic interactions is shown to scale with the position of halide atom in the periodic table, the heavier the element the larger is the anisotropy, in agreement with prior studies. Comparing the magnons for the bulk and single-layer CrI 3 , we find that the size of the topological gap becomes smaller in the latter case. The obtained next nearest-neighbor DM vector is oriented primarily in-plane of the monolayer and has relatively small z component, which results in a small value of the topological gap. Finally, we investigate finite-size effects in monolayers and demonstrate that the anisotropic couplings between Cr atoms close to the edges are much stronger than those in ideal periodic structure. This should have impact on the dynamics of the magnon edge modes in Cr halides.

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Section: B 2d Periodic Monolayerssupporting

confidence: 67%

Relativistic exchange interactions in CrX3 ( X=Cl , Br, I) monolayers

et al. 2020

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“…1 ). We point out that mixtures of Cl/Br (CrCl 3 − x Br x ) and Br/I (CrBr y I 3 − y ) have been reported before ( 18 ), but the three-halide series, the frustrated regime, and the bulk MM transition are presented here. We could not grow crystals of CrCl x I 3 − x due to the substantial size difference between Cl and I.…”

Section: Resultsmentioning

confidence: 71%

“…The color maps are produced by a linear interpolation between the 27 discrete data points, each represented by a black circle. Some of the two-halide samples are the same as in ( 18 ).…”

Section: Resultsmentioning

confidence: 99%

Accessing new magnetic regimes by tuning the ligand spin-orbit coupling in van der Waals magnets

et al. 2020

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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. Chromium trihalides provided the first such example with a change of interlayer magnetic coupling emerging upon exfoliation. Here, we take a different approach to engineer previously unknown ground states, not by exfoliation, but by tuning the spin-orbit coupling (SOC) of the nonmagnetic ligand atoms (Cl, Br, I). We synthesize a three-halide series, CrCl3 − x − yBrxIy, and map their magnetic properties as a function of Cl, Br, and I content. The resulting triangular phase diagrams unveil a frustrated regime near CrCl3. First-principles calculations confirm that the frustration is driven by a competition between the chromium and halide SOCs. Furthermore, we reveal a field-induced change of interlayer coupling in the bulk of CrCl3 − x − yBrxIy crystals at the same field as in the exfoliation experiments.

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“…The Cr 3+ ions are configured in a honeycomb network, and the green arrows represent the spin direction of Cr atoms, which are found to exhibit a strong ferromagnetic coupling. [ 39–44 ] The Raman spectra of Figure 1c indicates that the monolayer graphene still preserves a high crystal quality when heterostructured with CrBr 3 layer. The optical image in Figure 1d displays the as‐fabricated graphene/CrBr 3 heterostructures, along with the H‐shape Hall bar structure for conducting non‐local measurements.…”

Section: Figurementioning

confidence: 99%

Magnetic Proximity Effect in Graphene/CrBr₃ van der Waals Heterostructures

et al. 2020

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the third method, that is, the introduction of magnetism in graphene with the proximity effect in the interface of magnetic insulators and graphene. Pioneer works have been demonstrated with 3D bulk magnetic insulators like yttrium iron garnet, europium (II) sulfide, and bismuth ferrite. [7][8][9][10][11][12][13][14][15] Due to the short-range nature of the magnetic exchange coupling, a fully 2D van der Waals heterostructures is desired for downsizing the device and introducing magnetic proximity effect (MPE) at the same time. The recent profound discoveries of 2D ferromagnets [16][17][18][19][20][21][22][23][24][25][26][27][28][29] bring the possibility of 2D ferromagnetic van der Waals heterostructures, [30][31][32][33][34][35][36] it is urgent and essential to comprehensively investigate the magnetic coupling between graphene and 2D ferromagnetic materials for developing 2D spintronic devices. Not just the evidence of the existence of MPE in 2D ferromagnetic van der Waals heterostructures, [37,38] here, we report the direct observation of MPE in graphene/CrBr 3 van der Waals heterostructures by probing Zeeman spin Hall effect (ZSHE) through non-local transport measurements. A further quantitative estimation of Zeeman splitting field demonstrates a significant magnetic proximity exchange field even in a low magnetic field. Furthermore, we observe anomalous longitudinal resistance changes at the Dirac point R XX,D with increasing external magnetic field near ν = 0. This may attribute to the MPE induced ground state phases transformation of graphene from the ferromagnetic state at the lower magnetic field and a canted antiferromagnetic state at a higher field in quantum Hall regime.A typical graphene/CrBr 3 van der Waals heterostructure with Hall bar structure for electrical transport measurement is fabricated as shown in Figure 1a. In order to reach the best performance and a substantial MPE in graphene/CrBr 3 heterostructures, we optimize the fabrication process and conditions to achieve the desired heterostructures (see Experimental Section for details). The sample in the final stage is encapsulated and protected by poly(methyl methacrylate) (PMMA), which keeps the device surface away from the moisture and air for cryotemperature tests. The atomic structure of layered CrBr 3 is shown in Figure 1b. The Cr 3+ ions are configured in a honeycomb network, and the green arrows represent the spin direction of Cr atoms, which are found to exhibit a strong ferromagnetic coupling. [39][40][41][42][43][44] The Raman spectra of Figure 1c indicates that the monolayer graphene still preserves a high crystal quality when heterostructured with CrBr 3 layer. The optical image in 2D van der Waals heterostructures serve as a promising platform to exploit various physical phenomena in a diverse range of novel spintronic device applications. 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 implemen...

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Controlling Magnetic and Optical Properties of the van der Waals Crystal CrCl₃₋_xBr_x via Mixed Halide Chemistry

Cited by 120 publications

References 30 publications

Relativistic exchange interactions in CrX3 ( X=Cl , Br, I) monolayers

Relativistic exchange interactions in CrX3 ( X=Cl , Br, I) monolayers

Accessing new magnetic regimes by tuning the ligand spin-orbit coupling in van der Waals magnets

Magnetic Proximity Effect in Graphene/CrBr₃ van der Waals Heterostructures

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Controlling Magnetic and Optical Properties of the van der Waals Crystal CrCl3−xBrx via Mixed Halide Chemistry

Cited by 120 publications

References 30 publications

Relativistic exchange interactions in CrX3 ( X=Cl , Br, I) monolayers

Relativistic exchange interactions in CrX3 ( X=Cl , Br, I) monolayers

Accessing new magnetic regimes by tuning the ligand spin-orbit coupling in van der Waals magnets

Magnetic Proximity Effect in Graphene/CrBr3 van der Waals Heterostructures

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Product

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Controlling Magnetic and Optical Properties of the van der Waals Crystal CrCl₃₋_xBr_x via Mixed Halide Chemistry

Magnetic Proximity Effect in Graphene/CrBr₃ van der Waals Heterostructures