Nanoscale structural evaluation of 0-3 magnetic nanocomposites fabricated by electro-infiltration

Abstract

Magnetic nanocomposites with 0-3 connectivity, whereby a 0D magnetic nanoparticle phase is embedded into a 3D magnetic metal matrix phase, have gained increased interest for use in applications ranging from integrated power inductor cores to exchange-spring magnets. The electro-infiltration process, in which a metal phase is electroplated through a nanoparticle film phase, is an inexpensive approach compatible with semiconductor fabrication methods for the formation of these nanocomposites. Past demonstrations of electro-infiltrated nanocomposites have relied on scanning electron microscopy and energy dispersive x-ray spectroscopy to evaluate the 0-3 composite structure. However, a detailed investigation of the boundary between the particle and metal matrix phases cannot be performed with these tools, and it is unknown whether the particle/matrix interfaces are dense and void-free. This detail is critical, as the presence of even nanoscale voids would affect any potential magnetic exchange coupling and hence the overall electromagnetic properties of the material. This work seeks to explore the phase boundary of 0-3 magnetic nanocomposite fabricated by electro-infiltration by using scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy to analyze the nanostructure of two different composites—a nickel/iron-oxide composite and a permalloy/iron-oxide composite. High-resolution imaging indicates that the interface between the particle phase and matrix phase is dense and void-free. These results will help guide future studies on the design and implementation of these magnetic nanocomposites for end applications.

0‐3 magnetic nanocomposites via EPD: Current status for power component fabrication and future directions

“…Magnetic nanocomposites composed of two or more ferromagnetic or ferrimagnetic materials are gaining popularity for their applications in electronic device components, exchange-spring magnets, and micro-electromechanical system (MEMS) actuators. [14][15][16][17][18][19] For example, the combination of hard magnetic FePt nanoparticles in a soft magnetic phase such as Fe 2 O 3 has been used to increase the energy density of permanent magnetic materials. 15 Similarly, MEMS actuators have been fabricated using BaFe 12 O 19 nanoparticles in a CoNiPt alloy, which possess a high-energy product and strong coercive field to generate a large but stable magnetic torque for actuation.…”

“…Therefore, the consolidation of nanoparticles first into a thick film and then secondly using a method of infiltrating those films with the secondary magnetic material while maintaining the magnetic properties is of utmost importance. Although the deposition of magnetic nanoparticle films is the main focus of this perspective, it is important to note that the method for infiltrating porous magnetic nanoparticle films with another magnetic material (electro-infiltration EI]) was extensively studied by Smith et al 14,22 and Wen et al 24,26,27 for this purpose. We will begin our discussion with the deposition of magnetic nanoparticles into thick, physically stable and porous films, ultimately using electrophoretic deposition (EPD).…”

“…This method must consider the stability of the already deposited nanoparticle film during infiltration, as stress is introduced in the film as the infiltration continues, so that typically films greater than 4 μm cannot be infiltrated. 14,22 This stress-induced thickness limitation will be addressed in this work by a multilayered approach with subsequent iteration of EPD and EI steps to increase the thickness of the composite with the aforementioned goal of increasing power handling of the core. 32 Finally, future directions for 0-3 magnetic nanocomposites are offered, with emphasis on potential materials synthesis techniques.…”

“…Magnetic nanocomposites composed of two or more ferromagnetic or ferrimagnetic materials are gaining popularity for their applications in electronic device components, exchange‐spring magnets, and micro‐electromechanical system (MEMS) actuators 14–19 . For example, the combination of hard magnetic FePt nanoparticles in a soft magnetic phase such as Fe 2 O 3 has been used to increase the energy density of permanent magnetic materials 15 .…”

“…utilizes a typical electroplating set‐up to “infiltrate” the porous nanoparticle film with the electroplated metal of choice. This method must consider the stability of the already deposited nanoparticle film during infiltration, as stress is introduced in the film as the infiltration continues, so that typically films greater than 4 μm cannot be infiltrated 14,22 . This stress‐induced thickness limitation will be addressed in this work by a multilayered approach with subsequent iteration of EPD and EI steps to increase the thickness of the composite with the aforementioned goal of increasing power handling of the core 32 .…”