Characterization of Micro-Magnetic Thin Films on Oscillators and Effects of Varying Angle of Applied Field*

We report the further development of a fiber-optic interferometer system with variable applied DC and AC magnetic fields for the characterizations of micromagnets & micromagnetic films on small AFM oscillators. The system has measured and calibrated displacements to determine the resonant frequencies(~0.8-800 kHz), quality factors(~30-2000), amplitudes (0.001-10 nm) and spring constants (~0.1 N/m) of resonances. The driven response to AC magnetic field gradients (~1x10-4 - 1x10-3 T/m) has provided direct measurement of the dependence of the magnetic force on the angle of the applied field. Improvements in precision for angles of applied fields has let us measure a resonant frequency shift of δω/ω = ~10^{-3} for thin films with a 90 degree shift in angle of a polarizing field. The difference between a direct force Anti-Helmholtz geometry and a more strongly torsionally driven Helmholtz geometry has also been explored. This work supports our studies in nuclear magnetic resonance force microscopy (NMRFM).