Magnetism of nanostructured hematite: from cultural heritage to fundamental properties

Abstract

This study presents a comprehensive magnetic and morpho-structural investigation of α-Fe₂O₃ nanostructures from two distinct origins: natural (geologically extracted) and synthesized (i.e., laboratory-synthesized by an auto-combustion sol–gel method and commercially purchased hematite). All samples underwent thermal treatments, designed to reproduce color changes typical of hematite pigments in archaeological contexts. Through a combination of DC magnetization measurements and Mössbauer spectroscopy, we demonstrated the possibility of differentiating the origin of hematite nanostructures based on their magnetic behavior. Interestingly, low-temperature NPD analysis revealed that the intensity of the magnetic peak (003) was partially suppressed but not completely extinguished as expected for a perfect antiferromagnetic alignment, which suggests a possible coexistence of weakly ferromagnetic and antiferromagnetic phases in distinct domains below the Morin transition.