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Jia Wang, Zahra Ahmadi, David Lujan, Jeongheon Choe, [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), Xiaoqin Li, Jeffrey E. Shield, Xia Hong

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[Physical Vapor Transport Growth of Antiferromagnetic CrCl            <sub>3</sub>            Flakes Down to Monolayer Thickness](https://mdr.nims.go.jp/datasets/52ecc33d-21f8-4c9f-93de-be632e668ca0)

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Physical Vapor Transport Growth of Antiferromagnetic CrCl3 Flakes Down to Monolayer ThicknessRESEARCH ARTICLEwww.advancedscience.comPhysical Vapor Transport Growth of Antiferromagnetic CrCl3Flakes Down to Monolayer ThicknessJia Wang, Zahra Ahmadi, David Lujan, Jeongheon Choe, Takashi Taniguchi,Kenji Watanabe, Xiaoqin Li, Jeffrey E. Shield, and Xia Hong*The van der Waals magnets CrX3 (X = I, Br, and Cl) exhibit highly tunablemagnetic properties and are promising candidates for developing noveltwo-dimensional (2D) spintronic devices such as magnetic tunnel junctionsand spin tunneling transistors. Previous studies of the antiferromagneticCrCl3 have mainly focused on mechanically exfoliated samples. Controlledsynthesis of high quality atomically thin flakes is critical for their technologicalimplementation but has not been achieved to date. This work reports thegrowth of large CrCl3 flakes down to monolayer thickness via the physicalvapor transport technique. Both isolated flakes with well-defined facets andlong stripe samples with the trilayer portion exceeding 60 μm have beenobtained. High-resolution transmission electron microscopy studies showthat the CrCl3 flakes are single crystalline in the monoclinic structure,consistent with the Raman results. The room temperature stability of theCrCl3 flakes decreases with decreasing thickness. The tunnelingmagnetoresistance of graphite/CrCl3/graphite tunnel junctions confirms thatfew-layer CrCl3 possesses in-plane magnetic anisotropy and Néel temperatureof 17 K. This study paves the path for developing CrCl3-based scalable 2Dspintronic applications.1. IntroductionSince their discovery, two-dimensional (2D) van der Waals (vdW)magnets CrX3 (X = Cl, Br, I) have attracted extensive re-search interests for their unusual magnetic properties[1–10] com-pared with conventional magnetic metals and oxides.[11–13] Theyare flexible, can sustain the magnetic ground state down toJ. Wang, X. HongDepartment of Physics and Astronomy & Nebraska Center for Materialsand NanoscienceUniversity of Nebraska-LincolnLincoln, NE 68588-0299, USAE-mail: xia.hong@unl.eduThe ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/advs.202203548© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.This is an open access article under the terms of the Creative CommonsAttribution License, which permits use, distribution and reproduction inany medium, provided the original work is properly cited.DOI: 10.1002/advs.202203548monolayer thickness,[6,7,9,10] and can bestacked with other vdW materials to createmultifunctional heterostructures.[1–6,14–18] Ithas been shown that the magnetic or-der and magnetic anisotropy of CrX3can be sensitively tuned by strain anddoping,[16–19] making it a versatile play-ground for studying magnetic quantumphase transitions and designing novelenergy-efficient spintronic devices, includ-ing magnetic tunnel junctions,[1–5] spintunneling field–effect transistors,[16–18] andquantum spin Hall systems.[15] CrCl3 isan A-type antiferromagnet with in-planemagnetic anisotropy.[1–4] Previous studieshave mainly focused on mechanically exfo-liated samples.[1–5,8,20,21] While nanosheetsof CrCl3 have been deposited via the chem-ical vapor transport (CVT) method, onlysamples thicker than 25 nm have beenobtained.[22] Controlled synthesis of high-quality atomically thin flakes is of great fun-damental and technological interests buthas not been achieved to date.In this work, we report the direct growth of large CrCl3 flakesdown to monolayer thickness via the physical vapor transport(PVT) technique. Triangular and hexagonal thin flakes with well-defined facets as well as long stripe samples with the trilayerportion exceeding 60 μm have been obtained. High-resolutiontransmission electron microscopy (HRTEM) studies show thatthe CrCl3 flakes are single crystalline with the monoclinic struc-ture, consistent with the Raman characterizations. The sampleZ. Ahmadi, J. E. ShieldDepartment of Mechanical and Materials EngineeringUniversity of Nebraska-LincolnLincoln, NE 68588-2526, USAD. Lujan, J. Choe, X. LiDepartment of PhysicsUniversity of Texas at AustinAustin, TX 78712-1192, USAT. TaniguchiInternational Center for Materials NanoarchitectonicsNational Institute for Materials Science1-1 Namiki, Tsukuba, Ibaraki 305-0044, JapanK. WatanabeResearch Center for Functional MaterialsNational Institute for Materials Science1-1 Namiki, Tsukuba, Ibaraki 305-0044, JapanAdv. Sci. 2023, 10, 2203548 © 2022 The Authors. Advanced Science published by Wiley-VCH GmbH2203548 (1 of 7) 21983844, 2023, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202203548 by Cochrane Japan, Wiley Online Library on [27/01/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://crossmark.crossref.org/dialog/?doi=10.1002%2Fadvs.202203548&domain=pdf&date_stamp=2022-12-01www.advancedsciencenews.com www.advancedscience.comFigure 1. Synthesis of thick to monolayer CrCl3 flakes. a) Schematic of the experimental setup for PVT growth of CrCl3. b-d) Optical images of as-grownCrCl3 flakes on b) SiO2/Si, c) HOPG, and d) mica substrates. e–i) AFM images of CrCl3 flakes on mica with different thicknesses (upper panels), withthe height profiles along the dashed lines (lower panels). The averaged flake thicknesses are 24.8 ± 0.2 nm, 9.25 ± 0.04 nm, 1.84 ± 0.01 nm (trilayer),0.63 ± 0.07 nm (monolayer), and 1.9 ± 0.1 nm (trilayer), respectively.stoichiometry has been confirmed by scanning electron mi-croscopy (SEM)-energy dispersive X-ray spectroscopy (EDS) stud-ies. Atomic force microscopy (AFM) studies show that the roomtemperature stability of CrCl3 flakes decreases with decreasingthickness. Characterization of graphite/CrCl3/graphite tunnel-ing devices reveals a Néel temperature (TN) of 17 K and in-planemagnetic anisotropy in few-layer CrCl3. Our study enables scal-able synthesis of high-quality atomically thin CrCl3 flakes, pavingthe path for their implementation in 2D spintronic applications.2. Results and Discussion2.1. Synthesis of CrCl3 Flakes2D vdW CrCl3 flakes are synthesized from CrCl3 powder us-ing the PVT technique (Figure 1a, see Experimental Section forgrowth details). The samples are deposited on three types ofsubstrates: mica (fluorophlogopite, [KMg3(AlSi3O10)F2]), highlyoriented pyrolytic graphite (HOPG), and SiO2/Si substrates. Wethen investigate the effects of substrates on the lateral size, flakethickness, and crystalline orientation of the samples. As shown inFigure 1b, CrCl3 on SiO2/Si prefers vertical growth and forms rel-atively thick crystals. Horizontal growth of large size thin flakeshas been achieved on HOPG (Figure 1c) and mica (Figure 1d)substrates, which can be attributed to their atomically smoothand dangling-bond-free surfaces. Previous studies have shownthat such surfaces can effectively promote the attachment of pre-cursors on the layer edges and facilitate subsequent horizontalgrowth.[23,24] As the flakes deposited on HOPG do not have well-defined facets (Figure 1c) and are hard to isolate from the under-neath graphite pieces, we next focus on characterizing the sam-ples deposited on mica.We have obtained both isolated flakes with triangular andhexagonal shapes and long stripe samples on mica. Figure 1e–i shows the AFM topography images of five CrCl3 samples withdifferent thicknesses. The flakes thicker than 9 nm show well-defined facets with sharp edges (Figure 1e,f). The few-layer tomonolayer CrCl3 flakes (Figure 1g,h) also possess the triangu-lar shape, but the edges are rough with micro-facets and thecorners are rounded. This has been attributed to the CrCl3desorption during growth. For ultrathin flakes, there is an in-sufficient growth time for the edge atoms to reach thermody-namic equilibrium.[25] In previous studies, CVT-grown CrCl3nanosheets are mostly thicker than 25 nm,[22] and ultrathin flakeshave only been obtained via mechanical exfoliation.[1–5,20] Ourstudy is the first report of direct growth of monolayer CrCl3 (Fig-ure 1h). Systematic AFM imaging on a large scale reveals over25% yield of ultrathin flakes, including monolayer, bilayer, andtrilayer samples (Figure S1a,b, Supporting Information). In ad-dition to the isolated flakes, we have also achieved long stripesof ultrathin CrCl3 samples. Figure 1i shows the trilayer portion(66 μm by 20 μm) of a long stripe sample, whose overall lengthis over 1 mm (Figure S1c, Supporting Information). The ultra-thin portion of the stripe samples can exceed 60% (Section S1,Supporting Information).We examine the room temperature stability of the CrCl3 flakesby taking a series of AFM images with time after growth.[20,26]It has been shown that CrCl3 is more stable compared withCrI3.[20,21,26] For a 64 nm flake, there is no obvious change in thesample morphology for about 5 months (Figure S2a, SupportingInformation), showing excellent room temperature stability. Thethinner flakes, on the other hand, show clear degradation withtime. The 20 nm flake remains stable on Day 23, while bubble-like features emerge on the sample surface on Day 37 (FigureS2b, Supporting Information). Similar degradation signs haveAdv. Sci. 2023, 10, 2203548 © 2022 The Authors. Advanced Science published by Wiley-VCH GmbH2203548 (2 of 7) 21983844, 2023, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202203548 by Cochrane Japan, Wiley Online Library on [27/01/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advancedscience.combeen reported in exfoliated CrCl3 flakes,[20,26] which is attributedto the formation of CrCl2.[26] For the monolayer flakes, the samplesurface becomes rough on Day 6 (Figure S2c, Supporting Infor-mation), with the flake thickness increasing from 0.69 to 3.05 nm(Figure S2d, Supporting Information). It is possible that the sam-ple degradation has started even before it becomes discernable inAFM measurements, as previously reported in Cr2Ge2Te6.[27]2.2. Sample CharacterizationWe carry out TEM, SEM, and Raman measurements to charac-terize the sample structure and stoichiometry. Our studies showthat CrCl3 can be easily damaged when exposed to electron beamand laser excitation (Figure S3, Supporting Information). To en-sure the data quality, we have reduced the exposure time andused minimal laser power in these measurements and focusedon characterizing relatively thick samples (>20 nm). At roomtemperature, CrCl3 possesses the monoclinic structure, whichbelongs to the C2/m space group (Figure 2a).[28] The Cr atomsform a honeycomb structure in the a-b plane, with each Cr atomsurrounded by the Cl octahedron. Figure 2b shows an HRTEMimage of CrCl3, where the crystalline planes of (020), (11̄0), (1̄1̄0)make a quasi-equilateral triangle. The inter-planar spacing d isabout 5.1 Å, agreeing with the expected lattice parameter for themonoclinic structure. The corresponding selected area diffrac-tion (SAD) pattern (Figure 2c) is also consistent with the mon-oclinic crystal structure.[28] The sharp diffraction peaks and theabsence of impurity phases confirm the high crystallinity of thesample.The stoichiometry of the sample is investigated using SEM-EDS (Figure 2d–f). Element mapping of the Cr K-line (Figure 2e)and Cl K-line (Figure 2f) reveals a homogeneous distribution.From the EDS spectrum, we extract a Cr/Cl ratio of 0.304 (FigureS4, Supporting Information), reasonably close to the ideal ratioof 1/3 considering the uncertainties related to EDS quantitativeanalysis, as there is significant background signal from the un-derlying substrate for thin film samples.[22] No signal of sulfuris detected in the EDS spectrum, confirming that the sample pu-rity is not affected by the S powder used for promoting samplenucleation.Next, we carry out Raman studies at room temperature. Tominimize the sample damage by laser heating,[29] we transferthe samples onto Au-coated SiO2/Si substrates to facilitate en-ergy dissipation. Figure 3a shows the Raman spectra of CrCl3flakes with different thicknesses. For micron-thick bulk samples,we observed six Raman peaks at about 123, 165, 207, 244, 300,and 344 cm−1, which are denoted as Ag(1), Ag(2), Ag(3)/Bg, Ag(4),Ag(5), and Ag(6) modes, respectively. The spectrum agrees withthe monoclinic structure of CrCl3.[3,20] The Raman signal de-creases with sample thickness and becomes hard to resolve inflakes thinner than 20 nm. For the signal that can be detected,there is no noticeable peak shift with flake thickness.Figure 3b shows the polarized Raman spectra taken on a 43 nmCrCl3 flake. Compared with the polarized Raman spectra of bulkCrCl3 crystal,[30] we only resolve five Ag phonon modes in theparallel polarization (XX) and one Bg mode in the perpendicu-lar polarization (XY) due to the relatively low signal strength inthin flakes. The peak position for the Bg mode (about 207 cm−1)Figure 2. Structural characterization and element analysis of CrCl3 flakes.a) Schematic unit cell of monoclinic CrCl3, with a = 5.959 Å, b = 10.321 Å,c = 6.114 Å, 𝛼 = 𝛾 = 90o, and 𝛽 = 108.49°. b) HRTEM micrograph andc) SAD pattern taken on a thick CrCl3 flake along [001] zone axis. d) SEMimage of a thick CrCl3 flake, with element mapping of e) Cr and f) Cl.contains two modes Bg(3/4) with degenerate energy.[30] Figure 3cshows the polar maps of XX Raman intensity for the four Agmodes with relatively high intensity, where the angle of the in-cident light polarization 𝜃 is defined with respect to the a-axisof CrCl3 (Figure S5, Supporting Information). All Ag modes ex-hibit twofold symmetry, with four local maxima occurring at𝜃 = 0°, 90°, 180°, 270°. The intensity at 0° and 180° is higherthan that at 90° and 270°. The Raman intensity is proportionalto |gsR̃gTi |2, where gi (gs) is the polarization vector of the inci-dent (scattered) light and R̃ is the Raman tensor.[31] In the XXconfiguration, gs = gi∝(cos𝜃, sin𝜃, 0). For a monoclinic struc-ture, the angular-dependent Raman response in XX is given by:I(Ag)∝|acos2𝜃 + bsin2𝜃|2 and I(Bg)∝e2sin2(2𝜃), where a, b, and eare fitting parameters.[31] Previous studies have shown that bothAg and Bg modes can contribute to the polar mapping,[31] so theoverall Raman intensity can be expressed as:I′ ∝ |||acos2𝜃 + bsin2𝜃|||2 + e2sin2 (2𝜃) (1)Adv. Sci. 2023, 10, 2203548 © 2022 The Authors. Advanced Science published by Wiley-VCH GmbH2203548 (3 of 7) 21983844, 2023, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202203548 by Cochrane Japan, Wiley Online Library on [27/01/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advancedscience.comFigure 3. Raman characterizaiton of CrCl3 flakes. a) Raman spectra of CrCl3 flakes with different thicknesses. b) Raman spectra of a 43 nm CrCl3 flakemeasured in parallel (XX) and perpendicular (XY) configurations. Inset: Schematic of crystalline orientations and laboratory coordinates, where therelative angle ϕ between x-axis and sample a-axis is arbitrary. c) Polar plots of integrated Raman intensity for different Ag modes of the same CrCl3 flakeshown in (b).As shown in Figure 3c, Equation (1) well describes the angulardependence of Raman intensity, further confirming that CrCl3 iscrystallized in the monoclinic structure.2.3. Characterization of Few-Layer CrCl3 Tunnel JunctionsTo probe the magnetic properties of the sample, we fabricate few-layer CrCl3 into tunnel junction devices (Figure 4a) and character-ize their tunneling magnetoresistance (TMR). Figure 4b showsa device composed of a 6-layer CrCl3 tunnel barrier (Figures S6and S7, Supporting Information) sandwiched between top andbottom thin graphite flakes transferred on a SiO2 substrate withprepatterned gold electrodes (Experimental Section). The effec-tive area of the tunnel junction is about 10.8 μm2. The device isthen encapsulated by a top h-NB flake to avoid ambient degrada-tion. At room temperature, the I–V characteristic of the device ishighly stable for over 2 months in the ambient conditions, whichis the duration of measurement (Figure S8, Supporting Informa-tion).Figure 4c shows the tunneling characteristic of the device atvarious temperatures. The tunneling current decreases rapidlywith decreasing temperature below 300 K and exhibits weaktemperature-dependence below 50 K. Plotting I/V2 versus 1/Vreveals two distinct regimes, which can be understood by con-sidering the evolution of the dominating tunneling mechanism.At low bias V <<Φ/e, where Φ is the tunnel barrier height ande is the elementary charge, the tunneling current is dominatedby the direct tunneling mechanism, with the tunneling currentgiven by:[32,33]I ∝ Ve(− 2d√2m∗Φℏ)(2)Here m* is the effective mass, h̄ is the reduced Plank constant,and d is the thickness of the CrCl3 flake. At V > Φ/e, the Fowler–Nordheim (FN) mechanism becomes dominant, and the currentcan be expressed as:[32,33]I ∝ V2e(− 4d√2m∗Φ33ℏeV)(3)Equations (2) and (3) can well capture the data shown in Fig-ure 4c. The transition voltage between these two regimes de-creases with increasing temperature, illustrating the enhancedcontribution of thermo-carriers tunneling through the bias-modified tunnel barrier.[34]We then use the transition between the direct and FN tun-neling regimes at low temperature to estimate the tunnel bar-rier height Φ.[32,35] In Figure 4d, we plot ln( IV2) versus 1/V at2 K and superimpose the fitting curves for the direct tunnelingregime, i.e., ln( IV2) ∝ ln( 1V) (Equation (2)), and the FN regime,i.e., ln( IV2) ∝ 1V(Equation (3)). The transition voltage Vt is definedas the crossing point of these two behaviors (Vt ≈ 0.51 V), whichhas been used to estimate the height of the tunnel barrier. Asthe transition is relatively broad, this can lead to about 10% un-certainty in the estimated Φ. Assuming Φ = eVt = 0.51 eV andconsidering the layer number of the flake to be 6 ± 1 (Figure S7,Supporting Information), we extract the effective mass for theCrCl3 tunnel barrier to be m* = (0.5 ± 0.1)m0, where m0 is thefree electron mass.[36]Figure 4e shows the tunneling I–V relation at 2 K with andwithout a perpendicular magnetic field B⊥. Applying a magneticfield increases the tunneling current, which can be attributed tospin alignment in CrCl3 induced by the magnetic field. Withoutthe magnetic field, the spins in the adjacent layers are antiparallelto each other, which suppresses the electron tunneling probabil-ity, yielding an effectively higher tunnel barrier height. An ap-plied field of 6 T can align the spins of all layers along the out-of-plane direction, resulting in higher I. At V = 0.8 V, the tunnelingcurrent changes from 8.4 nA at 0 T to 25.6 nA at 6 T, correspond-ing to a TMR (6 T) = 100% × I(6 T)− I(0 T)I(0 T)= 206%, which is sig-Adv. Sci. 2023, 10, 2203548 © 2022 The Authors. Advanced Science published by Wiley-VCH GmbH2203548 (4 of 7) 21983844, 2023, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202203548 by Cochrane Japan, Wiley Online Library on [27/01/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advancedscience.comFigure 4. Tunneling characteristic of a graphite/6-layer CrCl3/graphite de-vice encapsulated with h-BN. a) Device schematic. b) Optical image. c)Zero field I/V2 versus 1/V at 300, 250, 200, 50, 25, 22, 20, 18, 12, and 2 K.The dashed line serves as a guide to the eye. d) Zero field ln(I/V2) versus1/V at 2 K with fits to Equations (2) and (3) (dashed lines). e) TunnelingI–V at 2 K with B⊥ = 0 and 6 T. Inset: Schematic of spin orientation in CrCl3with and without magnetic field.nificantly higher than that obtained on bilayer and trilayer CrCl3tunneling devices at this temperature in previous experiments.[5]The enhanced TMR shows that the spin filtering efficiency in-creases with increasing tunnel barrier thickness.[2]From the temperature-dependence of zero field tunneling cur-rent and its derivative dI/dT (Figure 5a), we identify a clear kinkat 17 K, which corresponds to the TN. The TN value is consistentwith previous reports of bulk[21] and exfoliated CrCl3.[1,2,4,5] Belowand above TN, the tunneling current exhibits distinct magneticfield dependence. As shown in Figure 5b, at 2 K, I rises rapidlywith increasing magnetic field and saturates at around B⊥ = 2.5 T.Below TN, the magnetic field aligns the in-plane, anti-aligned in-terlayer spins to the out-of-plane orientation, which yields highertunneling current.[1,2,4,5] Once the spins are fully aligned, increas-ing the magnetic field no longer changes the tunneling current.At 17 K, in contrast, the tunneling current exhibits a weaker mag-netic field dependence and does not saturate in field up to 6 T.Above TN, the spins do not have long-range order and are ran-domly oriented. The magnetic field is thus not sufficient to fullyalign the spins. This change is also reflected in the temperature-dependence of TMR at 6 T (Figure 5b inset), which decreasesmonotonically with increasing temperature and exhibits a deflec-tion point around TN. We also note that the change of tunnelingcurrent below TN is gradual, in contrast to the sharp change ob-served in CrI3.[6] This is consistent with the weak in-plane mag-netic anisotropy for CrCl3, where the out-of-plane magnetic fieldFigure 5. Tunneling magnetotransport of the 6-layer CrCl3 tunnel junc-tion device. a) Temperature-dependent tunneling current at zero magneticfield. b) Tunneling current versus B⊥ at 2 and 17 K. V = 0.8 V. Inset: TMRratio versus T at B⊥ = 6 T. The dotted line marks TN.induces continuous spin rotation rather than directly flipping thespin orientation.[1,2,4,5,21]3. ConclusionIn conclusion, we have successfully synthesized large CrCl3flakes down to monolayer thickness using the physical vaportransport technique, with high crystallinity and homogeneouschemical composition achieved. With h-BN encapsulation, few-layer CrCl3-based tunneling devices exhibit high ambient stabil-ity for more than 2 months. The tunneling magnetoresistancereveals that few-layer CrCl3 flakes possess a Néel temperature of17 K, in-plane magnetic anisotropy, and tunneling magnetoresis-tance of >200% below TN. Our study enables the direct growthof large size atomically thin CrCl3 flakes, paving the path for im-plementing this material for scalable 2D spintronic applications.4. Experimental SectionSynthesis: High-quality 2D vdW CrCl3 flakes were deposited in a hor-izontal single-zone furnace (Thermo Scientific TF55035-A1) with a 1 inchdiameter quartz tube by the PVT technique. A quartz boat with CrCl3Adv. Sci. 2023, 10, 2203548 © 2022 The Authors. Advanced Science published by Wiley-VCH GmbH2203548 (5 of 7) 21983844, 2023, 3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202203548 by Cochrane Japan, Wiley Online Library on [27/01/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advancedscience.comsource powder (99.99%, Alfa Aesar) was placed at the center of the single-zone tube furnace. A small amount of sulfur powder (99.9995%, Alfa Ae-sar) was loaded in the upstream of the tube to facilitate sample nucleation.The substrate was placed in the tube at about 10 cm downstream fromthe CrCl3 source powder. Three types of substrates, mica (highest gradeV1 mica disc, MIT), HOPG (Grade 3, SPI), and 300 nm SiO2/Si were in-vestigated. Before growth, the system was purged by Ar gas three times.During sample growth, the furnace was heated up to 700–750 °C at a rateof 30 °C min−1 with 40 standard cubic centimeters per minute (sccm)Ar process gas, and the tube was kept at one atmosphere pressure. After5 min growth, the furnace was cooled down to room temperature naturally.Sample Characterizations: The thickness and surface morphology ofas-grown CrCl3 flakes were characterized by AFM (Bruker Multimode 8)with the tapping mode. SEM was performed using an FEI Helios Nanolab660 with a field emission gun at 2 kV. The chemical element analysis wasconducted by EDS using the point and mapping modes in SEM. HRTEMstudies were performed in an FEI Tecnai Osiris electron microscope oper-ated at 200 kV. Nonpolarized Raman spectra were collected by a ThermoScientific DXR Raman microscope with a 532 nm laser, a 100× objective,exposure time of 30 s, 0.2 mW laser power, and a 900 lines mm−1 grat-ing. Polarized Raman spectra were recorded using a Harina/PrincetonActon 7500i/spectrometers equipped with a 532 nm laser, with a 50×objective, 0.2 mW incident laser power, integration time of 20 min, and1800 lines mm−1 grating. The excitation laser and collected Raman signalwere collinearly polarized. For the angular dependence measurements, theangle step was 5° for a half-wave plate, which was 10° in the polar map. ForSEM, TEM, and Raman characterizations, the CrCl3 flakes were transferredonto Au-coated (10 nm) SiO2/Si substrates (SEM and Raman) and TEMchips (Silicon Nitride Support Film, 50 nm with 0.5 × 0.5 mm Window)using the all-dry stamping transfer technique.Device Fabrication and Electrical Characterizations: Au/Cr (20/5 nm)electrodes were prepatterned into two-point geometry on SiO2/Si sub-strates using photolithography followed by e-beam evaporation. The tun-nel junction devices were assembled by the all-dry stamping transfermethod, which was performed on an optical microscope equipped witha stamping stage. The as-grown CrCl3 flakes were picked up from themica substrate by an elastomeric film (Gel-Film WF × 4 1.5 mil fromGelPak), which was adhered to a glass slide fixed on the stampingstage. The thin graphite electrodes and the h-BN protection layer weremechanically exfoliated. The graphite, few-layer CrCl3, and h-BN flakeswere picked up sequentially by gel-films and stacked into h-BN encapsu-lated graphite/CrCl3/graphite heterostructures on top of the prepatternedSiO2/Si substrates (Section S6, Supporting Information). The electricalmeasurements were carried out in a Quantum Design PPMS using an ex-ternal Keysight 1500A Semiconductor Device Parameter Analyzer.Supporting InformationSupporting Information is available from the Wiley Online Library or fromthe author.AcknowledgementsThe authors would like to thank Qiuchen Wu, Bingqiang Wei, Alexey Li-patov, and Alexander Sinitskii for their technical support. This work wassupported by NSF through Grant Nos. DMR-2118828, DMR-1710461, andOIA-2044049. T.T. acknowledges support from the JSPS KAKENHI (GrantNos. 19H05790 and 20H00354) for h-BN growth. The research was per-formed, in part, in the Nebraska Nanoscale Facility: National Nanotech-nology Coordinated Infrastructure, the Nebraska Center for Materials andNanoscience, and the Nanoengineering Research Core Facility, which aresupported by NSF ECCS: 2025298, and the Nebraska Research Initiative.Conflict of InterestThe authors declare no conflict of interest.Author ContributionsX.H. conceived the project. X.H. and J.W. designed the experiments. J.W.carried out sample deposition, AFM and SEM characterizations, devicefabrication, and magnetotransport studies. Z.A. and J.E.S. performed theTEM studies. J.W., D.L., J.C., and X.L. conducted the Raman studies.T.T. and K. W. contributed to the h-BN samples. J.W. and X.H. wrotethe manuscript. All authors discussed the results and contributed to themanuscript preparation.Data Availability StatementThe data that support the findings of this study are available in the sup-plementary material of this article.KeywordsCrCl3, physical vapor transport, tunnel junction, tunneling magnetoresis-tance, van der Waals magnetReceived: June 21, 2022Revised: October 7, 2022Published online: December 1, 2022[1] H. H. Kim, B. Yang, S. Li, S. Jiang, C. Jin, Z. Tao, G. Nichols, F. Sfigakis,S. Zhong, C. Li, S. Tian, D. G. Cory, G. X. Miao, J. Shan, K. F. Mak, H.Lei, K. Sun, L. Zhao, A. W. Tsen, Proc. Natl. Acad. Sci. USA 2019, 116,11131.[2] H. H. Kim, B. Yang, S. Tian, C. Li, G. X. Miao, H. Lei, A. W. Tsen, NanoLett. 2019, 19, 5739.[3] D. R. Klein, D. MacNeill, Q. Song, D. T. Larson, S. Fang, M. Xu, R. A.Ribeiro, P. C. Canfield, E. Kaxiras, R. Comin, P. Jarillo-Herrero, Nat.Phys. 2019, 15, 1255.[4] Z. Wang, M. Gibertini, D. Dumcenco, T. Taniguchi, K. Watanabe, E.Giannini, A. F. Morpurgo, Nat. 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