Hybrid Ni‐Co‐Ni Structures Prepared by Magnetophoresis as Efficient Permanent Magnets for Integration into Micro‐Electro‐Mechanical‐Systems

The direct integration of performant permanent magnets (PMs) within miniaturized circuits remains both a scientific and a technological challenge. Magnetophoresis-driven capillary assembly of hard magnetic nanoparticles is a promising approach to fabricate 3D rare-earth-free PMs. However, this process implies the use of soft magnetic blocks to generate the magnetic field gradients required to localize the assembly directly onto silicon substrates. The impact of these soft elements onto the overall magnetic properties is evaluated using Co nanorods as hard material and 150 mu m-thick Ni blocks. As expected, the presence of Ni softens the overall properties of the hybrid magnet obtained, but PM properties are preserved for reduced Ni volumes. Magnetic induction as high as 19mT at a distance of 200 mu m is generated by the hybrid Ni-Co-Ni structures, allowing for the electromagnetic actuation of a microelectromechanical resonant sensor.