Quantitative measurement of magnetic moments with a torsional resonator: Proposal for an ultralow moment reference material

Abstract

We present a method for defining the magnetic moment of a reference material based on a torsional resonator with a patterned magnetic film on its surface. Given accurate measurements of the magnitude of the applied field, the moment of inertia of the resonator, and the magnetic stiffening effect of the film on the resonance frequency of the resonator, we can obtain an absolute measurement of the anisotropy energy and magnetic moment of the film independently. With this approach, the anisotropy energy and the magnetic moment of the film are measured directly, eliminating the need for a detailed knowledge of the film's saturation magnetization or sample volume. In principle, all of the measurements needed for the reference material are traceable to an atomic clock frequency reference. We have performed preliminary measurements on Ni_0.8Fe_0.2 films patterned in a circle of 4.17 mm diameter. Representative samples had measured moments of 5.04±0.12 υA m² for nominal film thicknesses of 500 nm.