Micromechanical torque magnetometer with sub-monolayer sensitivity
Dong-Hoon Min, Andrew McCallum, Stephen E. Russek, John M. Moreland
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 sensitivity for a Ni0.8Fe0.2 film and for a Ni0.8Fe0.2/Cu multilayer film is less than 0.1 nm.