Fabrication and Characterization of CoFe2O4 and MnFe2O4 Nanomagnetic Thin Films for RF Applications

In order to have magnetic films with better radio frequency (RF) properties that can be utilized in a wide range of microwave devices and circuits, such as frequency selective limiters, tunable filters, and antennas, this paper presents the fundamental studies on ferromagnetic resonance (FMR) of magnetic nanoparticles, the fabrication process of the magnetic nanoparticle films, and the scattering parameters measurement results of the magnetic nanoparticle films on a microstrip RF line. We explore the FMR profiles of various magnetic nanoparticles and their corresponding magnetic susceptibilities. Two novel methods, the layer-by-layer (LbL) process and the solution cast (SC) method, are proposed to deposit cobalt ferrite (CoFe
₂
O
₄
) and manganese ferrite nanoparticles (MnFe
₂
O
₄
) on soda-lime glass substrates to fabricate magnetic films with various thicknesses (2.5–
$125~\mu \text{m}$
). In addition, a 3-D printed RF transmission line integrating the magnetic film is used to test the effect of the magnetic nanoparticles. By comparing the measured group delays of microstrip lines with different films, we can obtain some insights into the relationship of the magnetic film thickness, types of magnetic materials, deposition methods, and the amount of the group delay. Specifically, thicker films result in higher group delay, and the SC method is more efficient in fabricating thicker films than the LbL process. The fill factor of these two methods, however, shows that the LbL process generates higher particle loading in the films, while the SC films have considerably more organic binders inside to maintain them. Given the same film thickness, manganese ferrite nanoparticles bring higher group delay than the cobalt ferrite nanoparticles. This paper proposes new methods of fabricating thicker nanomagnetic films and explores the characterization of different magnetic materials with various film thicknesses. It, therefore, paves the way for fabricating monolithic microwave devices and circuits utilizing nanomagnetic materials.