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Probing the impact of magnetic interactions on the lattice dynamics of two-dimensional Ti2X (X=C,N) MXenes

Abstract

Dynamical properties of the two-dimensional Ti2C and Ti2N MXenes have been investigated by density functional theory and discussed in connection with their structures and electronic properties. To elucidate the influence of magnetic interactions on the fundamental properties of these systems, the nonmagnetic, ferromagnetic and three distinct antiferromagnetic spin arrangements on titanium sublattice have been considered. Each magnetic configuration has also been studied at two directions of the spin magnetic moment with respect to the MXene layer. The zero-point energy motion, following from the phonon calculations, has been taken into account while analyzing energetic stability of the magnetic phases against the nonmagnetic solution. This contribution was found not to change a sequence of the energetic stability of the considered magnetic structures of Ti2X (X=C, N) MXenes. Both Ti2X (X=C,N) systems are shown to prefer antiferromagnetic arrangement of spins between Ti layers and ferromagnetic order within each layer. This energetically privileged phase is semiconducting for Ti2C and metallic for Ti2N. The type of magnetic order as well as the in-plane or out-of-plane spin polarizations have relatively small impact on the structural parameters, Ti-X bonding length, force constants and phonon spectra of both Ti2X systems, leading to observable differences only between the nonmagnetic and any other magnetic configuration. Nonetheless, noticeable effect of the spin orientation on degeneracy of the Ti-3d orbitals is encountered.. The differences are revealed only between the nonmagnetic and any other magnetic configuration. The magnetic interactions affect, however, to a great extent the positions and intensities of the Raman-active modes, and hence one could exploit this effect for experimental verification of the theoretically predicted magnetic state of Ti2X monolayers. Theoretical phonon spectra of the Ti2X (X=C,N) MXenes exhibit linear dependence on energy in the long-wavelength limit, which is typical for a 2D system.

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Publication details

The article was received on 10 Dec 2017, accepted on 14 Feb 2018 and first published on 14 Feb 2018


Article type: Paper
DOI: 10.1039/C7CP08270C
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Probing the impact of magnetic interactions on the lattice dynamics of two-dimensional Ti2X (X=C,N) MXenes

    M. Sternik and U. D. Wdowik, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C7CP08270C

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