Apr 8, 2025
3:45pm - 4:00pm
Summit, Level 4, Room 442
Peter Kratzer1,Mohammad Amirabbasi1
University of Duisburg-Essen1
The two-dimensional van der Waals (vdW) materials MPS
3 (M=Mn, Fe, Co, Ni) display antiferromagnetic ordering of the magnetic moments at the transition metal ions. The possibility to exfoliate thin layers that preserve the magnetic order makes these materials interesting for numerous applications in devices that require integration of flexible patches of magnetic materials, e.g. in antiferromagnetic spintronics. Hence, an improved understanding of their magnetic properties is desirable.
Here, we parameterize spin Hamiltonians for monolayers of all four materials of this class using density functional theory plus Hubbard
U calculations [1]. We provide a step-by-step guide for calculating the magnetic exchange interactions and magnetic anisotropy energy using the (non-)collinear DFT+
U(+ SOC) approach with a suitably chosen
U for each material. The
U parameters have been optimized to match experimental band gaps, resulting in values of 3.0 eV for Mn, 2.22 eV for Fe, 3.0 eV for Co, and 5.57 eV for Ni, respectively. Although all materials are characterized by divalent magnetic ions on a honeycomb lattice, the filling sequence of the 3d orbitals results in different spin patterns in the ground state. Geometry optimization reveals that only in case of FePS
3 the honeycombs get distorted. Specifically, the Fe-Fe distances between nearest neighbors vary by 0.14 Å, and we obtain two different exchange terms along the longer and shorter bond distances. FePS
3 also sticks out among the other materials by displaying a large orbital moment and a magnetization perpendicular to the 2D plane [2].
It is found that the biquadratic interactions gain in importance while moving through the 3d series. MnPS
3, with its Néel ground state, behaves like a typical magnetic semiconductor where the exchange interactions fall off with distance. The Néel temperature for the 2D monolayer obtained from our Monte Carlo simulations is 73.6 K, which closely aligns with the experimental value of 78 K observed in the bulk system. For the other materials, featuring AFM zigzag chains, the third-nearest-neighbor exchange interaction is crucial for stabilizing this ground state, especially in the case of NiPS
3. We obtain Néel temperatures of 70, 86.5 and 94 K for FePS
3, CoPS
3 and NiPS
3, respectively.
Retaining the leading terms of a Holstein-Primakoff-transformed spin Hamiltonian, magnon spectra are calculated. While MnPS
3 is found to be an almost isotropic antiferromagnet with a tiny gap, the biquadratic interaction opens an increasingly wider gap for FePS
3, CoPS
3 and NiPS
3. In line with this observation, our Monte Carlo simulations demonstrate that the biquadratic interactions contribute a 20 to 30% rise to the Néel temperatures of CoPS
3 and NiPS
3. In summary, our computational work provides evidence for a systematically improved first-principles description of these promising materials using a carefully chosen DFT+
U approach and an extended magnetic Hamiltonian.
[1] M. Amirabbasi and P. Kratzer, Phys. Rev. Mater. 8 (2024) 084005
[2] M. Amirabbasi and P. Kratzer, Phys. Rev. B 107 (2023) 024401