Micromechanical torque magnetometer with sub-monolayer sensitivity

We have developed a micromechanical torque sensor with sub-monolayer sensitivity for in situ monitoring of the magnetic moment of thin films during deposition. The film is deposited onto a microcantilever. The torque on the film is determined by measuring the deflection of the cantilever due to a small AC magnetic field perpendicular to the surface of the film. The microcantilevers have a high mechanical quality factor, large surface area, low spring constant, and high resonance frequency to improve film sensitivity to thickness. A phase-locked loop minimizes the resonance frequency shift of the cantilever due to mass loading and temperature drift that would otherwise affect the measurement of magnetic torque. The demonstrated thickness sensitivity for a Ni0.8Fe0.2 film and a Ni0.8Fe0.2/Cu multilayer film is less than 0.1 nm.