Anisotropy and magnetostriction measurement by interferometry

Extending the use of a laser-Doppler interferometer that measures magnetostriction by measuring the deflection of a thin-film cantilever sample to also measure the anisotropy is reported. When the sample is driven with a rotating magnetic field of constant magnitude, a number of harmonics of twice the rotating field frequency are evidence of the magnetization vector lagging and leading the drive field around the sample. Altering the magnitude of the drive field so that the H vector traces out an ellipse is found to null the harmonic signals. This ellipse has its major axis aligned with the hard axis. Using the Stoner–Wohlfarth single-domain-particle model, it is shown that a rotating field will cause the magnetization to rotate around the particle uniformly only if the difference in magnitude between the fields along the major and minor axes is equal to the anisotropy field. Measurements on isotropic and anisotropic samples confirm the theory.