Nanomechanical and Optomechanical Torque Magnetometry of Isolated Nanomagnetic Assemblies

Abstract

Nanomechanical torque magnetometry is emerging as a highly-sensitive method for gauging magneto-statics and magnetic dynamics in mesoscopic and nano-scale magnetic materials. Advances in torque magnetometry are presented here, which were unattainable using previ- ous techniques. Silicon nitride membrane-based nanomechanical torque magnetometers were first fabricated and characterized using the resonance modes and magnetic hysteresis and integrated with ∼ 350 bacterial magnetosome nanoparticles in a random assembly. Methods of assembling the magnetic materials (nanoparticles, mesoscopic magnetic disks) in geometrical shapes on the nanomechanical torque magnetometers were developed later on. Further, optomechanical torque magnetometers were developed to derive their highly sensitive transductions in ambient conditions. Optomechanical torque magnetometers were also used as RF susceptometers to acquire the vector-based susceptibility components. Finally, RF susceptometry was combined with the torque-mixing resonance spectroscopy for characterization of magnetic dynamics. The new nanophotonic optomechanical torque magnetometers developed in this Thesis can potentially be used for probing the magnetization, susceptibility, and spin resonances in a countable number of magnetic nanoparticles, leading to single spin detection in ambient conditions.