Magnetic properties of stage-1 CoCl2-graphite intercalation compounds diluted with MgCl2.

Abstract

We report a detailed study of the dilution of the magnetic properties of stage-1 ${\mathrm{CoCl}}_{2}$-graphite intercalation compounds (GIC's) with nonmagnetic ${\mathrm{MgCl}}_{2}$. The substitution of magnetic ions by nonmagnetic ions reduces the three-dimensional antiferromagnetic ordering temperature ${\mathit{T}}_{\mathit{N}}$, and reduces the low-temperature transition field ${\mathit{H}}_{\mathit{t}}$ that is a measure of the antiferromagnetic interlayer coupling. The intercalate layer in the stage-1 ${\mathrm{Co}}_{\mathit{x}}$${\mathrm{Mg}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cl}}_{2}$-GIC's fills only 85% of the available volume of the intercalate gallery. The extrapolated value of the Co concentration, ${\mathit{x}}_{\mathit{p}}$=0.65, at which ${\mathit{H}}_{\mathit{t}}$ and ${\mathit{T}}_{\mathit{N}}$ go to zero, suggests that the 15% concentration of voids is distributed randomly throughout the intercalate layer. It is proposed that for x\ensuremath{\ge}0.65 there is a connected magnetic two-dimensional triangular lattice. Our indirect measurement of the in-plane intercalate distribution is in agreement with recent transmission-electron-microscopy studies that show there is a connected network of intercalate with a structural coherence length as large as 1 \ensuremath{\mu}m.