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

We report the result of a novel structural-, electronic- and magnetic-investigation of exfoliated highlyoriented-pyrolytic-graphite (HOPG) samples exhibiting distorted-moire-superlattices. Field-dependentmagnetometry 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 similar to 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 similar to 77 K highlighted an unusual broadening in the van Hove singularities, possibly a confirmation of disorder-induced-ferromagnetism. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Automated summary

This study presents a novel investigation of the structural, electronic, and magnetic properties of exfoliated highly oriented pyrolytic graphite samples, revealing anomalous magnetic hysteresis and response phenomena. The observed anomalies include a transition from vortex-like ferrimagnetic hysteresis to ferromagnetic behavior, as well as broadening van Hove singularities pointing to disorder-induced ferromagnetism.