Magnetic Functionalization of High- Q Mechanical Resonators with Co3Fe Nanopillars for Spin-Mechanical Coupling

Abstract Coupling electronic spin degrees of freedom to the motion of micromechanical resonators could enable quantum-enhanced force sensing, the exploration of macroscopic non-Gaussian states, and information transduction for hybrid quantum systems. A promising route exploits Zeeman shifts of spin states induced by the displacement of resonators functionalized with magnetic nanostructures. However, established nanomagnet fabrication methods, such as thin-film patterning, are incompatible with the inherently fragile nature of microresonators. Here, we report the successful growth of soft-ferromagnetic Co3Fe pillars, with a 500 nm diameter and 2000 nm height, on 50 nm thick SiN trampoline membranes by focused electron beam induced deposition (FEBID). We show that this functionalization preserves mechanical quality factors up to 7 × 106, confirming that the FEBID process is noninvasive to the resonator. Using nitrogen-vacancy scanning magnetometry, we probe the magnetic properties of a pillar in external fields up to 15 mT and observe a clear opening of its hysteresis loop, indicative of ferromagnetic behavior with a small but finite coercivity. At an NV-Co3Fe pillar apex distance of ∼300 nm we directly measure magnetic field gradients of 3 × 104 T m–1.