We have developed a mechanical method for modulating sample magnetization in magnetic resonance force microscopy experiments. A small-amplitude, low-frequency dithering of a magnetic field gradient source relative to a sample is used to create an oscillating magnetic field at the sample, which leads to a modulation of magnetization in rf-irradiated samples by magnetic resonance. Using this technique in concert with modulating rf power, we have achieved a 10 000ϫ decrease in a

more »

... g spurious response of microcantilevers to rf fields in sample-on-cantilever magnetic resonance force microscopy experiments. This mechanical implementation of "anharmonic modulation" is especially well suited for low power and vacuum applications, and is unique in its ability to modulate sample magnetization in magnet-on-cantilever experiments where the cantilever frequency is found to be a strong function of magnetic field. © 1999 American Institute of Physics. ͓S0021-8979͑99͒02520-7͔ II. SAMPLE-ON-CANTILEVER MRFM As a first step towards implementing our approach, we performed sample-on-cantilever ESR MRFM with the apparatus sketched in Fig. 1͑a͒ . Before attaching the sample ͑or in subsequent experiments, a magnetic particle͒, bare-cantilever resonance frequency f 0 , quality factor Q 0 , and spring constant k 0 were determined by analysis of the cantilever Brownian motion spectrum, 13 where cantilever motion is measured with a fiber-optic interferometer. 14 After attaching the sample, the loaded-cantilever resonance frequency f c , a͒ Current address: