In the context of magnetic materials, ferrites are among the most extensively studied. This class of ceramic materials, which can be represented by the general structure M_xFe_yO_z, present an attractive set of properties: highly tunable coercivity and saturation magnetization, applicability at high frequencies and good corrosion resistance. According to the metal M that is employed for their manufacturing, properties can be soft or hard magnetic. This remarkable flexibility favors a wide range of applications, ranging from the realization of inductor cores and switches to the production of magnetic recording media and microelectromechanical systems (MEMS). In addition, ferrites are not based, unlike other hard magnetic materials like NdFeB or FePt, on the use of precious or strategic materials.

For applications like MEMS manufacturing and recording media manufacturing, ferrites must be deposited as thin layers and one of the most promising approaches to accomplish this task is the use of inkjet deposition (IJD). IJD, indeed, offers relevant advantages: low cost, optimal material usage, patterning capability. For example, inkjet has been employed for the deposition of soft magnetic NiZn-ferrites [1].

In the present work, cobalt ferrite (CoFe₂O₄) is deposited in the form of thin layers by mean of IJD onto silicon substrates. The coatings are then annealed to partially sinter the material and to increase the coercivity of the layers [2]. In order to deposit the material, stable suspensions of cobalt ferrite nanoparticles are synthesized, and their printability is assessed. The morphology of the printed layers is characterized from the microstructural and phase composition point of view. Finally, the magnetic properties of the material are characterized, evidencing maximum attainable coercivities in excess of 1600 Oe in the out-of-plane direction.

[1] M. Bissannagari et a., Ceram. Int. 41(6), 8023-8027 (2015)

[2] F. Cheng et al., Solid State Commun. 107(9), 471-476 (1998)