Oryong Kwon

A first-principles study of magnetism of lithium fluorosulphate LiFeSO4F

Magnetism of tavorite and triplite LixFeSO4F (x = 0, 1/2, and 1) has been studied using the first-principles density-functional theory. It was found that an antiferromagnetic ordering is more stable compared to a ferromagnetic state and the energy difference between two magnetic states is reduced when the lithium is intercalated, being consistent with a recent experimental observation of lowering Neel temperature from 100 K of FeSO4F to 25 K of LiFeSO4F. Furthermore, the magnetic moment of 3.8 μB/Fe for FeSO4F was found to be oriented along the [010], whereas that (4.3 μB/Fe) of LiFeSO4F along the [001]. And the magnetic moment and magneto-crystalline anisotropy were found to be insensitive upon different atomic structures, which imply that the lithium intercalation affects the spin orientation of Fe rather than the interplay between lattice and magnetism suggested by an experiment.

Magnetism and Magnetocrystalline Anisotropy of CoFe Thin Films: A First-principles Study

We investigate magnetism and magnetocrystalline anisotropy of CoFe thin films, using VASP code in GGA. In this study Coterminated and Fe-terminated 5-layer CoFe thin films are employed. The Co-terminated CoFe thin film shows two total energy minima at 2-dimensional lattice constants of 2.45 A and 2.76 A. The film of 2.45 A has fcc-like structure and the film of 2.76 A has bcc-like structure similarly to a bulk CoFe alloy. And the fcc-like film is more stable by the energy difference of about 160 meV compared to the bcc-like film. The Fe-terminated CoFe film shows very complicated behaviour of total energy which is suspected to be closely related to its complex magnetic structure. The Co-terminated CoFe film of 2.76 A shows perpendicular magnetocrystalline anisotropy (MCA), while the film of 2.45 does parallel MCA. The Fe-terminated CoFe film also exhibits similar MCA behaviour.

Thickness effect on magnetocrystalline anisotropy of Co/Pd(111) films: A density functional study

In this study, we carried out first-principles calculations on magnetocrystalline anisotropy (MCA) of Co/Pd thin films by adopting two different systems of (i) n-Co/3-Pd and (ii) n-Pd/3-Co. In one system, we vary the thickness of Co layer, fixing the thickness of the Pd layer to 3-monolayers, and in the other system vice versa. MCA is mainly governed by the surface and interface Co atoms, while contributions from other Co atoms are smaller. MCA energy (EMCA) of the Co/Pd thin film shows oscillatory behavior with the thickness of the Co layer, but is insensitive to the thickness of the Pd layer. In particular, the n-Co/3-Pd films of n = 2, 4, and 6 exhibit strong perpendicular MCA of about 1 meV. Our results suggest that controlling the thickness of the Co layer in Co/Pd (111) is crucial in achieving strong perpendicular MCA.