High frequency magnetic field imaging by frequency modulated magnetic force microscopy

Abstract

High frequency ac magnetic field from magnetic recording head was successfully imaged by using our newly developed frequency-modulated magnetic force microscopy (FM-MFM), which uses the frequency modulation of cantilever oscillation caused by applying ac magnetic field to a mechanically oscillated cantilever. The FM-MFM has been demonstrated and the experimental results show good agreement with our proposed models for FM-MFM. The amplitude and phase images of an ac magnetic field can be obtained separately by using the FM-MFM technique with a lock-in amplifier. By taking advantage of this technique, the present FM-MFM method opens a possibility to evaluate the magnetic field characteristics of magnetic recording head with high spatial resolution.

Secondary resonance magnetic force microscopy

“…Therefore, techniques for detecting an alternating magnetic field with high spatial resolution are of great importance. Recently, Saito et al [11][12][13] reported the frequency modulation MFM (FM-MFM) technique and showed that it could achieve a spatial resolution of 15 nm. In FM-MFM, the first resonant frequency of the cantilever vibration f 1 is modulated by the alternating magnetic field with frequency f m , and magnetic signals are obtained using a heterodyne method with a modulated frequency of f 1 À f m .…”

“…One solution for reducing this interference is to apply a phase-lock loop (PLL) circuit to maintain a constant frequency difference of f 1 À f m . 12,13 Another solution is to obtain the magnetic images using not f 1 but another resonant frequency such as the second resonant frequency. Recently, Venstra et al demonstrated Q-factor con-trol of a cantilever by mechanical sideband excitation at the sum (f 1 þ f 2 ) and difference (f 1 À f 2 ) frequencies.…”