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

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Science Advances  24 Jul 2020:
Vol. 6, no. 30, eabb9379
DOI: 10.1126/sciadv.abb9379
  • Fig. 1 Structure of the van der Waals alloys.

    The CrCl3−xyBrxIy alloys with a honeycomb-layered structure were synthesized by a CVT process from mixtures of CrCl3, CrBr3, and CrI3 in appropriate ratios. The gray, blue, green, and red spheres represent Cr3+, Cl, Br, and I, respectively. Cr3+ is a spin 3/2 ion with three electrons in the t2g manifold.

  • Fig. 2 Triangular phase diagrams as a function of Cl, Br, and I content.

    (A) Triangular phase diagram of TC as a function of composition in CrCl3−xyBrxIy with field in the plane (B). The star symbol near the center is a composition with 27% Cl (bottom axis), 40% Br (right axis), and 33% I (left axis), corresponding to Cr(Cl0.27Br0.40I0.33)3 = CrCl0.8Br1.2I1.0. (B) Triangular phase diagram of ΘW. 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).

  • Fig. 3 Magnetic susceptibility data.

    Representative Curie-Weiss analyses on CrCl0.8Br1.2I1.0 measured with field (A) parallel and (B) perpendicular to the honeycomb layers. The observation of a single sharp peak rules out disorder or chemical inhomogeneity (see also fig. S3). Both the zero field–cooled (ZFC; blue) and field-cooled (FC; red) data are presented. Solid green lines show the Curie-Weiss fit to the ZFC data. The Weiss temperature ΘW and effective moment μeff are comparable between the B and B configurations.

  • Fig. 4 Phase diagram of the magnetic frustration.

    Frustration index (f = ΘW/TC) as a function of composition in CrCl3xyBrxIy. This map is only a qualitative measure of frustration, especially since the f-index was originally proposed for isotropic (not anisotropic) magnets (19).

  • Fig. 5 Theoretical analysis of the magnetic anisotropy.

    (A) The magnetic anisotropy energy ∆ plotted as a function of Cl SOC (αCl) by fixing the SOC of Cr to unity (αCr = 1). (B) ∆ plotted as a function of the Cr SOC by switching off the Cl SOC (αCl = 0). (C) The anisotropy energy as a function of the SOC in Cr and Cl, showing a competition between in-plane and out-of-plane anisotropies tuned by αCr and αCl.

  • Fig. 6 MM transition in the bulk of VdW alloys.

    (A) Magnetization plotted as a function of field in CrCl0.8Br1.2I1.0. The red and blue data correspond to the field perpendicular (B) and parallel (B) to the honeycomb layers, respectively. The saturated moment is consistent with S = 3/2 in Cr3+. (B) Magnified view of the spin-canting transition at B = 0.7 T. (C) Optical image, scanning electron microscope (SEM) image, and energy-dispersive x-ray spectroscopy (EDX) color maps reveal a uniform distribution of Cr (yellow, K-edge), Cl (green, K-edge), Br (red, L-edge), and I (blue, L-edge) in CrCl0.8Br1.2I1.0. Photo credit: F.T., Boston College.

Supplementary Materials

  • Supplementary Materials

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

    Thomas A. Tartaglia, Joseph N. Tang, Jose L. Lado, Faranak Bahrami, Mykola Abramchuk, Gregory T. McCandless, Meaghan C. Doyle, Kenneth S. Burch, Ying Ran, Julia Y. Chan, Fazel Tafti

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    • Supplementary Text
    • Table S1
    • Figs. S1 to S5

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