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  • Letter

Antiferromagnetic fluctuations and orbital-selective Mott transition in the van der Waals ferromagnet Fe3−xGeTe2

Xiaojian Bai, Frank Lechermann, Yaohua Liu, Yongqiang Cheng, Alexander I. Kolesnikov, Feng Ye, Travis J. Williams, Songxue Chi, Tao Hong, Garrett E. Granroth, Andrew F. May, and Stuart Calder
Phys. Rev. B 106, L180409 – Published 30 November 2022
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    Abstract

    Fe3−xGeTe2 is a layered magnetic van der Waals material of interest for both fundamental and applied research. Despite the observation of intriguing physical properties, open questions exist even on the basic features related to magnetism: is it a simple ferromagnet or are there antiferromagnetic regimes, and are the moments local or itinerant. Here, we demonstrate that antiferromagnetic spin fluctuations coexist with the ferromagnetism through comprehensive elastic and inelastic neutron scattering and thermodynamic measurements. Our realistic dynamical mean-field theory calculations reveal that the competing magnetic fluctuations are driven by an orbital selective Mott transition (OSMT), where only the plane-perpendicular a1g orbital of the Fe(3d) manifold remains itinerant. Our results highlight the multi-orbital character in Fe3−xGeTe2 that supports a rare coexistence of local and itinerant physics within this material.

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    • Received 3 February 2022
    • Revised 26 August 2022
    • Accepted 8 November 2022

    DOI:https://doi.org/10.1103/PhysRevB.106.L180409

    ©2022 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    MagnetismSpin dynamics
    1. Physical Systems
    FerromagnetsVan der Waals systems
    1. Techniques
    DFT+DMFTInelastic neutron scatteringNeutron diffractionNeutron scattering
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Xiaojian Bai1,*, Frank Lechermann2,†, Yaohua Liu1, Yongqiang Cheng1, Alexander I. Kolesnikov1, Feng Ye1, Travis J. Williams1, Songxue Chi1, Tao Hong1, Garrett E. Granroth1, Andrew F. May3, and Stuart Calder1,‡

    • 1Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
    • 2Institut für Theoretische Physik III, Ruhr-Universität Bochum, D-44780 Bochum, Germany
    • 3Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

    • *baix@ornl.gov
    • †frank.lechermann@ruhr-uni-bochum.de
    • ‡caldersa@ornl.gov

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    Issue

    Vol. 106, Iss. 18 — 1 November 2022

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    Images

    • Figure 1
      Figure 1

      Elastic neutron scattering data showing FM and AFM static magnetic correlations in Fe2.85GeTe2. (a) Crystal structure and FM spin state of Fe2IFe1−xIIGeTe2. (b) Single layer view, where the Fe atoms form a decorated honeycomb lattice. The dashed lines indicate the unit cell. (c) Low-Q elastic scattering with l = 0.0±0.05 r.l.u. The white lines are Brillouin zone boundaries. The shaded region indicates the line cuts along the [110] direction integrated over k = 0.0±0.02 r.l.u., shown in the panel (d). Intensity at the (e) FM zone center Γ and (f) the AFM positions Q1 and Q2 as a function of temperature. Black and red curves are power-law fits of the data. A linear background are fitted and removed for order-parameter data at Q1 [Fig. S5]. The paramagnetic background at 250 K is removed at Q2 and the data offset by 200 for clarity.

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    • Figure 2
      Figure 2

      Inelastic neutron-scattering data of Fe2.85GeTe2 showing coexistence of FM and AFM excitations. The Bose factor is divided out in all panels, giving the imaginary part of the dynamical susceptibility χ′′. (a) Temperature dependence of energy- and momentum-resolved excitations at k = 0.5±0.05 r.l.u. and l = 0.0±0.3 r.l.u.. The optical modes around 10 and 20 meV are attributed to phonons, see Sec. S6 for comparison with DFT-calculated phonon spectra and Refs. [41, 42, 43, 44, 45, 46] therein for technical details. (b) Low-Q constant-energy cut at E = 4±1 meV. The white lines are Brillouin zone boundaries. (c) Line cuts along the [110] direction at k = 0.5±0.1 r.l.u. and E = 4±1 meV.

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    • Figure 3
      Figure 3

      DFT+DMFT results for Fe3−δGeTe2, where δ = x is the VCA doping level. (a) Total (left) and local Fe(3d) (spin-)orbital-resolved (right) spectral function A(ω) for different δ and T. Left insets: larger energy window. Black circle for T = 100 K highlights the OSMT scenario. (b) T-dependent Lindhard spin susceptibility χs(0)(q,ω = 0) for δ = 0.1,0.25. (c, d) k-resolved spectral-function properties for δ = 0.1. (c) A(k,ω) along high-symmetry lines in a Fe(3d) fatspec representation at T = 290 K. Mixed orbital weight appears as the accordingly mixed colors (see color scheme in graph). (d) Spin-summed A(k,ω) for T = 50 K. (e) kz = 0 FS for T = 290 K in fatspec representation (left) and spin-summed intensity for T = 50 K (right).

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