Multicomponent magnetic spinels: From complexity of crystal chemistry to coupled magnetic resonance imaging (MRI)

Spinels have a rich history that spans complexities of their structures to multitude of useful properties and intriguing phenomena. Herein, we demonstrate the versatility and elegance of ferrite-spinel based magnetic nanostructures (MNSs) as a contrast agent in magnetic resonance imaging (MRI). We show that the magnetic properties of the inverse spinel Fe₃O₄ MNS can be enhanced by tuning their crystal chemistry. After doping with Mn²⁺ and Zn²⁺ into Fe₃O₄ MNS at a right stoichiometry, high saturation magnetization and magnetic anisotropy were observed due to rearrangement and specific positions of Mn²⁺, Zn²⁺, Fe²⁺, and Fe³⁺ cations in the inverse spinel AB₂O₄ crystal lattice. The improved magnetic properties were leveraged to develop T₁-weighted MRI contrast agent that are more biocompatible and efficient than currently used Gd-based complexes. This work underscores the rich opportunities in magnetic spinels for not only unusual applications as in MRI contrast enhancement but also the complexity and versatility of its crystal chemistry that forms the basis for its diverse properties.