Fabrication of High Magnetic Susceptibility Nano‐FeS 2 via Electronic Reconstruction Induced by Alternating Magnetic Field

Magnetic materials, such as Ferumoxytol and Gd‐DTPA, have played an important role in biomedical areas. The relentless pursuit of novel magnetic materials that are clinically applicable is an eternal theme in biomedical engineering. Pyrite (FeS 2 ) is a mineral drug in China that has been used for a long history. Besides the inherent biocompatibility proved in the human body as well as the donor of H 2 S, pyrite also belongs to the family of transition metal dichalcogenides, which endows it with flexible functional tunability of magnetism to be a promising candidate for novel magnetic nanodrug. However, the nano‐FeS 2 synthesized by common coprecipitation often shows poor magnetic susceptibility, so its application has greatly been limited. Herein, we reported an innovative strategy to prepare nano‐FeS 2 with high magnetic susceptibility (HS‐nano‐FeS 2 ) via alternating magnetic field‐assisted coprecipitation. AMF treatment effectively regulated electronic reconstruction of Fe 2+ in nano‐FeS 2 without foreign‐element doping, and super‐exchange interaction is proposed as the dominant factor for the optimized magnetic susceptibility toward a favorable spin‐polarized configuration. The HS‐nano‐FeS 2 is suitable for long‐term MR angiography imaging with excellent biosafety. We believe HS‐nano‐FeS 2 provides a novel magnetic candidate for clinical translation and demonstrates an innovative strategy at the electronic level.