Anomalous vortex-shaped ferrimagnetic hysteresis in exfoliated highly oriented pyrolytic graphite with distorted moiré superlattices

Abstract

We report the result of a novel structural-, electronic- and magnetic-investigation of exfoliated highly-oriented-pyrolytic-graphite (HOPG) samples exhibiting distorted-moiré-superlattices. Field-dependent-magnetometry of pre-selected lamellae revealed the presence of an anomalous-transition occurring from a vortex-like-ferrimagnetic-hysteresis to a ferromagnetic-behavior as the maximum-field was increased from 10 Oe to 800 Oe (T∼ 250 K). The observed as-acquired hysteresis resembled those intrinsic-signals reported by Scheike et al. and Shuai et al. in superconductive- and ferrimagnetic-HOPG. We highlight an anomalous field-dependent-magnetic-response from 10 Oe to 200 Oe, as also evidenced by susceptibility-plots, with a ferromagnetic-transition occurring at 120 Oe. Further, scanning-tunneling-microscopy (STM) and scanning-tunneling-spectroscopy (STS) acquisitions at T∼77 K highlighted an unusual broadening in the van Hove singularities, possibly a confirmation of disorder-induced-ferromagnetism.