Single-molecule magnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>Mn</mml:mi><mml:mn>12</mml:mn></mml:msub></mml:math> on GaAs-supported graphene: Gate field effects from first principles

We study gate field effects on the heterostructure ${\mathrm{Mn}}_{12}{\mathrm{O}}_{12}{(\mathrm{COOH})}_{16}{({\mathrm{H}}_{2}\mathrm{O})}_{4}|\mathrm{graphene}|\mathrm{GaAs}$ via first-principles calculations. We find that under moderate doping levels, electrons can be added to but not taken from the single-molecule magnet ${\mathrm{Mn}}_{12}{\mathrm{O}}_{12}{(\mathrm{COOH})}_{16}{({\mathrm{H}}_{2}\mathrm{O})}_{4}$ (${\mathrm{Mn}}_{12}$). The magnetic anisotropy energy (MAE) of ${\mathrm{Mn}}_{12}$ decreases as the electron-doping level increases due to electron transfer from graphene to ${\mathrm{Mn}}_{12}$ and change in the band alignment between ${\mathrm{Mn}}_{12}$ and graphene. At an electron-doping level of $\ensuremath{-}5.00\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.16em}{0ex}}\text{cm}{}^{\ensuremath{-}2}$, the MAE decreases by about 18% compared with zero doping. The band alignment between graphene and GaAs is more sensitive to electron doping than to hole doping, since the valence band of GaAs is close to the Fermi level. The GaAs substrate induces a small band gap in the supported graphene under zero gate field and a nearly strain-free configuration. Finally, we propose a vertical tunnel junction for probing the gate dependence of MAE via electron transport measurements.