Research ArticleCONDENSED MATTER PHYSICS

Magnetism in semiconducting molybdenum dichalcogenides

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Science Advances  21 Dec 2018:
Vol. 4, no. 12, eaat3672
DOI: 10.1126/sciadv.aat3672
  • Fig. 1 ZF μSR time spectra and temperature-dependent ZF μSR parameters for MoTe2.

    ZF μSR time spectra for the single-crystal (A) and polycrystalline (B) samples of MoTe2 recorded at various temperatures up to 450 K. (C) Temperature dependence of the internal field μ0Hint of 2H-MoTe2 as a function of temperature. (D) Temperature dependence of the magnetic fractions VM and V* of the precession and strongly damped signals, respectively (see text). The total signal is also shown.

  • Fig. 2 Temperature-dependent weak-TF μSR parameters and weak-TF μSR spectra for MoTe2.

    (A) WTF μSR time spectra for MoTe2 recorded at T = 5 and 300 K. The solid gray lines represent fits to the data by means of Eq. 2. Temperature dependence of the oscillating fraction (B) and the paramagnetic relaxation rate λ (C) of the single-crystalline and polycrystalline samples of MoTe2 obtained from the weak-TF μSR experiments. The solid arrows mark the magnetic transition temperatures TM and T*. The solid gray lines represent fits to the data by means of phenomenological function (see Eq. 3 in Materials and Method).

  • Fig. 3 Temperature- and field-dependent magnetization data for MoTe2 and MoSe2.

    The temperature dependence of ZFC and FC magnetic moments of MoTe2 (A) and MoSe2 (C), recorded in an applied field of μ0H = 10 mT. The arrows mark the onset of the difference between ZFC and FC moment as well as the anomalies seen at low temperatures. The field dependence of magnetic moment of MoTe2 (B) and MoSe2 (D), recorded at various temperatures.

  • Fig. 4 Observation of intrinsic defects in 2H-MoTe2 through STM and sample characterizations.

    (A) Large-scale atomic-resolution STM topography (20 nm) of the MoTe2 surface. The image reveals an approximately uniform density of two types of defects over the entire surface. The STM topography was taken at −1.25 V and −100 pA set point. (B) Small-scale atomic-resolution STM topography (2 nm) shows that these two types of defects are mainly substitutional Mo atoms at Te sites (Mosub) and Mo vacancies (Movac). (C and D) Local STM topography (1 nm) and DFT + U–optimized geometry for Mosub defect, respectively. The observed atoms in (C) are those at the top layer of tellurium, with an increased topographic height profile at the center of the six brightest spots. We attribute this to a molybdenum replacement of a tellurium atom. (E and F) Local-scale STM topography (1 nm) and DFT + U–optimized geometry of the second type of defects observed, respectively. The image in (E) shows a depression in the topographic height profile, centered between three tellurium atoms. On the basis of the symmetry, we attribute this to a molybdenum vacancy under the layer of tellurium. (G) ESR spectra for 2H-MoTe2, recorded at various temperatures. (H) PDF average structure refinements for 2H-MoTe2 at 300 K fitted to the hexagonal 2H-structure model.

  • Fig. 5 DFT + U and STM.

    (A) Spin-polarized density of states, DOS(states/eV), of Mosub defects in the antiferromagnetic (AFM) phase. Fermi level, EFermi, is set to zero. Both the spin-up and spin-down DOS reveal an in-gap state due to the defect. (B) Magnetization density (±0.001 electrons/Bohr3) on the top surface of bulk 2H-MoTe2 in AFM configuration. Spin-up and spin-down states are shown in faint blue and orange isosurfaces, respectively. Note that spins also couple antiferromagnetically at the local level between the Mo impurity and the nearest Mo atoms. (C) Scanning tunneling spectroscopy dI/dVs taken on the two types of defect as well as far from any defect.

  • Fig. 6 Pressure evolution of various quantities.

    (A) Magnetic transition temperature TM and magnetic volume fraction VM as a function of pressure. (B) Pressure dependence of the magnetic fractions VM and V*, corresponding to the precession μSR signal and the strongly damped μSR signal, respectively. The total magnetic signal is also shown. The dashed lines are guides to the eyes.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/12/eaat3672/DC1

    Fig. S1. ZF μSR time spectra and temperature-dependent parameters for MoSe2.

    Fig. S2. The temperature dependence of the paramagnetic fraction for 2H-MoTe2 and 2H-MoSe2.

    Fig. S3. ESR signals for 2H-MoTe2 and 2H-MoSe2.

    Fig. S4. PDF results for 2H-MoTe2 and 2H-MoSe2.

    Fig. S5. Temperature and pressure evolution of the paramagnetic fraction Vosc.

    Fig. S6. Magnetization data for MoSe2 and MoTe2.

    Fig. S7. Hysteresis loop for MoSe2 and MoTe2.

    Fig. S8. Calculated magnetization of the antisite defect versus Hubbard U.

    References (4853)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. ZF μSR time spectra and temperature-dependent parameters for MoSe2.
    • Fig. S2. The temperature dependence of the paramagnetic fraction for 2H-MoTe2 and 2H-MoSe2.
    • Fig. S3. ESR signals for 2H-MoTe2 and 2H-MoSe2.
    • Fig. S4. PDF results for 2H-MoTe2 and 2H-MoSe2.
    • Fig. S5. Temperature and pressure evolution of the paramagnetic fraction Vosc.
    • Fig. S6. Magnetization data for MoSe2 and MoTe2.
    • Fig. S7. Hysteresis loop for MoSe2 and MoTe2.
    • Fig. S8. Calculated magnetization of the antisite defect versus Hubbard U.
    • References (4853)

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