Abstract
The intercalation of Fe into the van der Waals gap in the 2H phase transition-metal dichalcogenides , , and produces many interesting electronic, magnetic, and structural effects. The scanning tunneling microscope (STM) and atomic force microscope (AFM) prove to be very sensitive to these changes and we report a wide range of results as a function of Fe concentration. All three materials support similar 3×3 charge-density-wave (CDW) structures in the pure state at low temperatures. At low concentrations of Fe the CDW superlattice is still strong at 4.2 K and persists to high concentrations of Fe. At high concentrations, the Fe becomes ordered in the octahedral holes in the van der Waals gaps, and superlattices of the form 2×2 and √3 × √3 are observed. These can be detected at both 300 and 4.2 K. STM spectroscopy at 4.2 K shows that in 2H- and 2H- the energy gap in the electronic spectrum is initially reduced, but stabilizes at higher Fe concentrations and remains well defined for the ordered 2×2 phase. A transition from a CDW to a mixed CDW and spin-density-wave state is indicated, since these high Fe concentration phases are antiferromagnetic. In 2H- both 2×2 and √3 × √3 superlattices are observed. The 2×2 regions show a large energy gap, while the √3 × √3 do not. The latter phase is ferromagnetic and would not be expected to exhibit a gap. The development of the electronic structures over the entire range of Fe concentrations has been followed by STM and AFM and can be tracked in detail.
- Received 5 April 1993
DOI:https://doi.org/10.1103/PhysRevB.48.14543
©1993 American Physical Society