Apparent Ferromagnetism in Exfoliated Ultrathin Pyrite Sheets
Anand B. Puthirath, Aravind Puthirath Balan, Eliezer Fernando Oliveira, Vishnu Sreepal, Francisco C. Robles Hernández, Guanhui Gao, Nithya Chakingal, Lucas M. Sassi, Thibeorchews Prasankumar, Gelu Costin, Róbert Vajtai, Douglas S. Galvão, Rahul R. Nair, Pulickel M. Ajayan
Abstract
There has been no experimental evidence for ferromagnetic ordering in isotropic atomically thin two-dimensional crystals, until a bilayer Cr2Ge2Te6 and a three-atom thick monolayer CrI3 is shown to retain ferromagnetic ordering at finite temperatures. Here, we demonstrate successful isolation of a non-van der Waals-type ultrathin 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 are 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 sheets have a stable ferromagnetic ground state different from their diamagnetic bulk counterparts. This theoretical finding is evaluated by experimentally employing low-temperature superconducting quantum interference device measurements, and an anomalous ferromagnetic kind of behavior is observed.