Perpendicular magnetic anisotropy of iron-intercalated transition-metal disulfides studied by X-ray magnetic circular dichroism

Shibata, Goro 

Layered transition-metal dichalcogenides with the 1T-CdI-type crystal structure are known to exhibit a wide variety of electric and magnetic properties by intercalating various transition-metal atoms of different concentrations between adjacent layers. Among them, iron-intercalated titanium disulfides FeTiS and tantalum disulfides FeTaS are ferromagnets which exhibits strong perpendicular magnetic anisotropy (PMA) with large coercive fields of a few tesla. It is reported that FeTaS shows stronger PMA than FeTiS, presumably due to the stronger spin-orbit interaction (SOI) of Ta. In the present study, in order to elucidate the microscopic origin of the strong PMA in these compounds, the electronic structure and magnetism of single-crystalline FeTiS and FeTaS have been investigated via X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). From the spectral line shapes of XAS and XMCD, the valence of Fe is shown to be essentially 2+, whereas Ti is in an itinerant electronic state between 3+ and 4+. This shows that electrons are doped from the intercalated Fe atoms into the host TiS and TaS. Notably, clear differences in the spectral line shapes of XMCD at the Fe edges are observed between FeTiS and FeTaS despite the similarity of the crystal structures. This may be attributed to the different SOI strength between these compounds. Based on the configuration-interaction cluster-model calculations, the observed changes in the spectral line shapes can be qualitatively reproduced by virtually increasing SOI of Fe 3 electrons.