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First principles characterization of spinterfaces between magnetic Cobaltocene molecule and 2D magnets (CrI$_3$, Fe$_3$GeTe$_2$)

Nikola Machacova, Biplab Sanyal

Abstract

In this paper, we examine the properties of spin-polarized interfaces consisting of single-molecule magnet bis(cyclopentadienyl)cobalt(II) (cobaltocene) and two-dimensional magnetic materials, semiconducting CrI$_3$ and metallic Fe$_3$GeTe$_2$, using first-principles density functional theory based calculations. Our calculated adsorption energies indicate the stability of these hetero-interfaces with the observation of hybridization of electronic states across the interface. Magnetic exchange interaction parameters have been obtained from both total energy differences and the Liechtenstein-Katsnelson-Antropov-Gubanov (LKAG) formalism in the basis of maximally localized Wannier functions (MLWFs). Analysis of these parameters shows a strong directional anisotropy in the magnetic substrate-molecule interaction in agreement with the nature of orbital hybridization. Additionally, possible exchange mechanisms are proposed based on orbital-resolved exchange and hopping parameters. We also show that the molecular adsorption may enhance the intralayer exchange interactions, with some exchange parameters reaching up to a 3-fold increase in magnitude compared to the freestanding case. Finally, we observe a 100 % spin polarization at the Fermi level in the cobaltocene/CrI$_3$ interface, which makes it particularly promising for spin-transport applications.

First principles characterization of spinterfaces between magnetic Cobaltocene molecule and 2D magnets (CrI$_3$, Fe$_3$GeTe$_2$)

Abstract

In this paper, we examine the properties of spin-polarized interfaces consisting of single-molecule magnet bis(cyclopentadienyl)cobalt(II) (cobaltocene) and two-dimensional magnetic materials, semiconducting CrI and metallic FeGeTe, using first-principles density functional theory based calculations. Our calculated adsorption energies indicate the stability of these hetero-interfaces with the observation of hybridization of electronic states across the interface. Magnetic exchange interaction parameters have been obtained from both total energy differences and the Liechtenstein-Katsnelson-Antropov-Gubanov (LKAG) formalism in the basis of maximally localized Wannier functions (MLWFs). Analysis of these parameters shows a strong directional anisotropy in the magnetic substrate-molecule interaction in agreement with the nature of orbital hybridization. Additionally, possible exchange mechanisms are proposed based on orbital-resolved exchange and hopping parameters. We also show that the molecular adsorption may enhance the intralayer exchange interactions, with some exchange parameters reaching up to a 3-fold increase in magnitude compared to the freestanding case. Finally, we observe a 100 % spin polarization at the Fermi level in the cobaltocene/CrI interface, which makes it particularly promising for spin-transport applications.
Paper Structure (10 sections, 9 equations, 7 figures, 1 table)

This paper contains 10 sections, 9 equations, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. Computational Methods
  3. Results and Discussions
  4. Cobaltocene
  5. Structural properties
  6. Charge transfer
  7. Electronic properties
  8. Magnetic properties
  9. Conclusions
  10. Acknowledgments

Figures (7)

  • Figure 1: Final structures after optimization. Top view and side view of CrI$_3$ (a,c), Fe$_3$GeTe$_2$ (b,d) interfaces with cobaltocene. The atoms' colors are Cr (blue), I (purple), Fe (orange), Ge (light purple), Te (green), Co (pink), C (brown), and H (white).
  • Figure 2: Charge density differences between the deformed layers and the interface for CrI$_3$ (left), and Fe$_3$GeTe$_2$ (right). The corresponding isosurface levels are: $5.9 \cdot 10^{-4} \,e$ (CrI$_3$), $2.9 \cdot 10^{-4} \,e$ (Fe$_3$GeTe$_2$).
  • Figure 3: Spin-polarized total (a,d), element-projected (b,e), and orbital-decomposed (c,f) density of states close to the Fermi level for CoCp$_2$/CrI$_3$ (a--c) and CoCp$_2$/Fe$_3$GeTe$_2$ (d--f) interfaces. The (a,b,d,e) plots show a broader interval from -5 eV to 5 eV around the Fermi level ($E_F$ was set to zero), the (c,f) part provides a more detailed view of the states close to the Fermi level.
  • Figure 4: (a): Top view of the partial charge density for states between -0.2 eV and $E_F$ in the CrI$_3$ supercell, with isosurface level $10^{-3} \, e$ and Cr atoms labeled. (b): $J_{ij}$ interaction parameters as a function of distance between atoms $i$ and $j$ obtained from TB2J calculation. (c): Schematic visualization of an indirect exchange mechanism across the interface, where hoppings are denoted by red arrows.
  • Figure 5: (a): Top view of the FGT supercell with Fe atoms in the upper Fe layer labeled. (b): J$_{ij}$ interaction parameters as a function of distance between atoms $i$ and $j$ obtained from TB2J calculation. (c): Schematic visualization of an indirect exchange mechanism across the interface, where hoppings are denoted by red arrows.
  • ...and 2 more figures