  Experimental evidence for ferromagnetic ordering in isotropic atomically thin
two-dimensional crystals has been missing until a bilayer Cr2Ge2Te6, and a
three-atom thick monolayer CrI3 are shown to retain ferromagnetic ordering at
finite temperatures. Here, we demonstrate successful isolation of a non-van der
Waals type ultra-thin nanosheet of FeS2 derived from naturally occurring pyrite
mineral (FeS2) by means of liquid-phase exfoliation. Structural
characterizations imply that (111) oriented sheets are predominant and is
supported theoretically by means of density functional theory surface energy
calculations. Spin-polarized density theory calculations further predicted that
(111) oriented three-atom thick pyrite sheet has a stable ferromagnetic ground
state different from its diamagnetic bulk counterpart. This theoretical finding
is evaluated experimentally employing low temperature superconducting quantum
interference device measurements and observed an anomalous ferromagnetic kind
of behavior.
