  The dual-resonant enhancement of mechanical and optical response in cavity
optomechanical magnetometers enables precision sensing of magnetic fields. In
previous working prototypes of such magnetometers, a cavity optomechanical
system is functionalized by manually epoxy-bonding a grain of magnetostrictive
material. While this approach allows proof-of-principle demonstrations,
practical applications require more scalable and reproducible fabrication
pathways. In this work, we scalably fabricate optomechanical magnetometers on a
silicon chip, with reproducible performance across different devices, by
sputter coating a magnetostrictive film onto high quality toroidal
microresonators. Furthermore, we demonstrate that thermally annealing the
sputtered film can improve the magnetometer sensitivity by a factor of 6.3. A
peak sensitivity of 585 pT/Hz^1/2 is achieved, which is comparable with
previously reported results using epoxy-bonding.
