Printing rare-earth-free (REF) magnetic inks: synthesis, formulation, and device applications

Additive manufacturing (AM) of magnetic materials has recently attracted increasing interest for various applications but is often limited by the high cost and supply chain risks of rare-earth-element (REE) magnetic precursors. Recent advances in nanomanufacturing have enabled the development of rare-earth-free (REF) magnetic materials, such as spinel ferrites, hexaferrites, MnAl, MnBi, Alnico, FePt, and iron oxides/nitrides, which offer promising alternatives for printing high-performance magnetic devices. This review provides a detailed overview of the latest developments in REF magnetic materials, covering both synthesis strategies of REF magnetic materials/nanomaterials and their integration into AM processes. We summarize the design and formulation of magnetic inks, emphasizing the unique properties of REF ferromagnetic and ferrimagnetic systems and their adaptability to AM techniques like direct ink writing, inkjet printing, aerosol jet printing, and screen printing. Key advancements in materials chemistry, ink rheology, and device performance are discussed, highlighting how the structure of REF magnetic materials impacts device functionalities. This review concludes with a perspective on the pressing challenges and emerging opportunities in AM of REF magnetic inks. Through this review, we aim to offer insights into the structure-processing-property relationship of REF magnetic inks and guide the design of next-generation printable magnetic systems in a scalable, cost-effective, and sustainable manner.