Exfoliated Pyrite (FeS2)- a non-van der Waals 2D Ferromagnet

Two-dimensional (2D) magnetism has been highly sought after since the discovery of graphene, the first and most studied of all the 2D materials. However, experimental evidence for ferromagnetic ordering in isotropic 2D crystals has been missing until a three-atoms thick CrI3 was shown to retain ferromagnetic ordering at finite temperatures down to a monolayer. However, 2D ferromagnetic materials discovered so far are having a transition temperature which is much lower than room temperature and hence are not useful for device applications. Here, we demonstrate successful isolation of a non-van der Waals 2D material derived from naturally occurring pyrite mineral (FeS2) by means of liquid phase exfoliation in organic solvent. It is evident from the magnetic measurements that 2D FeS2 is ferromagnetic with long-range magnetic ordering extending even up to the room-temperatures, whereas bulk pyrite precursor is weakly paramagnetic. Transmission electron microscopy together with Raman spectroscopy and XPS measurements confirm the crystallinity and purity of 2D FeS2. Atomic force microscopy affirms the 2D nature of exfoliated flakes. Theoretical density functional theory calculations corroborate the experimental findings along with the stability of exfoliated 2D sheets which is of prime importance in the case of non-van der Waals exfoliation.