Magnetic nanocomposites have applications in power electronics, where properties such as high permeability, high thickness, high operating frequency, and low loss are desired. Recent work shows that electroinfiltration, where a magnetic composite is formed by electroplating a metal through a deposited nanoparticle layer, produces magnetic composites with high permeabilities and low losses [1]. However, electroinfiltration has a thickness limitation of &lt;4 μm. Attempts to overcome this by fabricating multiple composite layers have been demonstrated, but reveal a trade-off between composite thickness and maximum operating frequency [2]. This trade-off is due to dimensional resonance, caused by the formation of standing waves in the material cross-section. Laminations can be used to overcome this effect, as the resulting laminated layers have smaller cross-sections that increase the frequency at which standing waves begin to form [3]. This work demonstrates a process to create thick magnetic composites by laminating layers of infiltrated magnetic composite with insulating layers of parylene to reduce dimensional resonance effects, as seen in Figure 1. For the magnetic layer, composites made from iron-oxide nanoparticles infiltrated with nickel-metal are used. Four samples are made, containing 1, 2, 3, and 5 layers of magnetic composite, separated from each other by approximately 1-2.5 μm of parylene. Structural characterization of these samples was done using SEM with EDS capabilities, showing that the desired laminated structures were achieved. Next, dc magnetic characterization showed that the magnetic properties of the laminated composites remain nearly constant with the increase in thicknesses. Finally, ac magnetic measurements reveal that these laminated composites have a constant dimensional resonance of ~350 MHz irrespective of an increase in the number of layers, as seen in Figure 2. In conclusion, it is evident that laminating the nanocomposites reduces the effects of dimensional resonance, and a fabrication process for implementing laminations into electroinfiltrated composites has been demonstrated.

![](https://assets.underline.io/uploads/markdown_image/1/image/5ea576300cbef4d9bd7faac9c6149a5f.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/a047796add6514afab8b783c426ceed4.jpg)

Fabrication of thick, laminated, electroinfiltrated magnetic nanocomposites to reduce dimensional resonance effects

Fabrication of thick, laminated, electroinfiltrated magnetic nanocomposites to reduce dimensional resonance effects

Composite multiferroic materials represent a novel class of functional materials where multiple types of ferroic ordering coexist. Further, coupling between different types of ferroic materials can result in additional ordering, which can be leveraged to fabricate new multifunctional devices.1, 2 One-dimensional composite magnetoelectric nanofibers, free of substrate-based constraints provide an ideal platform for achieving magnetoelectric coefficients that are orders of magnitude greater than those in ideal thin films.3 Here, we will present the synthesis of one-dimensional magnetoelectric nanofibers via electrospinning followed by device assembly. Electrospinning can be used to fabricate composite nanowires in a range of configurations by varying the orientation of the piezoelectric and magnetoelectric phases, including random, core-shell, or Janus. Here, we will focus on the synthesis and assembly of bi-phasic magnetoelectric Janus nanofibers, this structure retains external access to each phase as well as to the interface, making them well suited to form modular structures (Figure 1). As-electrospun fibers are amorphous and form a continuous fiber network, requiring subsequent processing steps to both crystallize the nanofibers while also taking advantage of thermal stresses to break the nanofibers into shorter nanowires for device applications. The final nanowire length can be controlled by the electrospinning parameters (e.g., applied voltage) as well as the calcination ramp rate. Shorter nanowires (&lt;10 mm) result from as-spun nanofibers with a smaller initial diameter, and/or faster calcination ramp rates. Aligned arrays of the nanowires can then be assembled into device architectures via dielectrophoresis (Figure 1b-d). The efficiency of nanowire assembly via dielectrophoresis can be enhanced solvent choice as well as the frequency of the applied voltage. We found optimum assembly using butanol and an applied voltage of 42 volts peak to peak at a frequency of 5kHz. Additionally, prior to assembly it may be necessary to perform an acid rinse of the nanofibers to remove any undesired carbonate phases that may hinder assembly. This method results in a linear density of assembled nanowires of ~20 nanowires/mm. The assembled arrays of magnetoelectric nanowires can then be used for a variety of devices, including zero-power magnetic field and current sensors.4 Figure 2 shows the magnetoeletric coefficients of BaTiO3/CoFe2O4 nanowire arrays. These nanowire arrays have a magnetoelectric coefficient of 514+/- 27 mV cm-1 Oe-1 at 1 kHz, considerably larger than bulk values 104 mV cm-1 Oe-1. Figure 2 also shows corresponding device sensitivities. Magnetoelectric nanowires can be assembled into arrays for low power sensors, including magnetic field and current sensors and they can also be developed for biomedical applications where the remote delivery of electric fields is desired, such as for neural modulation.5 Here, we will demonstrate the versatility of magnetoelectric nanowires, their synthesis, and applications. This work opens new opportunities and applications for magnetoelectric materials. This work was support by the NSF I/UCRC on Multi-functional Integrated System Technology (MIST Center) IIP-1439644. The authors acknowledge the use of the Major Analytical Instrumentation Center (MAIC) and Nanoscale Research Facility (NRF) at the University of Florida.

**References:**

1. Spaldin, N. A., Proc. R. Soc. A 2020, 476 (2233), 20190542. 2. Nan, C.-W.; Dong, S.; Viehland, D.; Srinivasan, G., Journal of Applied Physics 2008, 103 (3), 031101. 3. Xie, S.-H.; Liu, Y.-Y.; Li, J.-Y., Front. Phys. 2012, 7 (4), 399-407. 4. Bauer, M. J.; Wen, X.; Tiwari, P.; Arnold, D. P.; Andrew, J. S., Microsystems & Nanoengineering 2018, 4 (1), 37. 5. Ferson, N. D.; Uhl, A. M.; Andrew, J. S., P. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 2020.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/5dbf229eb0b210860d8fcd24301da24c.jpg)
Figure 1. (a) scanning electron microscope image of a biphasic magnetoelectric nanowire suspended across an electrode gap (b) optical microscope image of an electrical assembly (c) a schematic magnetoelectric voltage source consisting of composite magnetoelectric nanowires and (d) a schematic of a possible architecture suitable if the density of the assembled nanowires is found to be generally uniform.

![](https://assets.underline.io/uploads/markdown_image/1/image/3c329a99c16139ffe78fbd2b64a3eabc.jpg)
Figure 2. Magnetoelectric coefficients and corresponding device sensitivities of BaTiO3/CoFe2O4 nanowire arrays as a function of frequency measured at angles of approximately no inductive effects, the angle of maximum constructive induction, and maximum destructive induction.

 Magnetoelectric Nanowires and Their Applications INVITED

**Session chair:** Guijun Li, Hong Kong University of Science and Technology



IOD - Power Devices, Induction

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Fabrication of thick, laminated, electroinfiltrated magnetic nanocomposites to reduce dimensional resonance effects

Magnetoelectric Nanowires and Their Applications INVITED

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