Percolative magnetic correlation and competing-antiferromagnetism in highly oriented pyrolytic graphite with hexagonal Moiré superlattices at the magic-angle

Occurrence of magnetic-correlation-phenomena in multi-layered carbon-materials has recently attracted an important attention for applications in magnetic devices and spintronics. In this study, exfoliated highly-oriented-pyrolytic-graphite (HOPG) lamellae exhibiting hexagonal-Moiré-superlattices, with periodicity of ∼13 nm (1st category, θ rot ∼ 1.09 ) and ∼36 nm (2nd category, θ rot ∼ 0.39°) were investigated. Raman-spectroscopy evidenced weak D, D' and intense G bands. In 1st category, magnetization versus field, ZFC- FC magnetic-curves from 2 K to 300 K and T-ESR revealed presence of uncorrelated and correlated ferromagnetic clusters at T∗ ∼ 150 K together with a critical transition at Tc ∼ 50 K, compatible with percolative-ferromagnetic-correlation. Comparative measurements on the 2nd category, revealed an analogue trend, with at T∗ ∼ 50-60 K together with an irreversibility at Tc ∼ 40 K, indicative of competing ferromagnetic/antiferromagnetic-correlations.