Towards a Magnetic Resonance Force Microscope Employing a Ferromagnetic Probe Mounted on the Force Detector

A crucial remaining challenge in the development of the magnetic resonance force microscope (MRFM) is to place the magnetic probe on the mechanical resonator. Here we address the problem of spurious detector response arising from interactions between the magnetic tip and various external applied elds. Ferromagnetic resonance experiments on a microscopic, thin-lm yttrium iron garnet crystal mounted on an atomic force microscope cantilever revealed the importance of ensuring that the induced magnetic moment of the magnetic tip is independent of the applied magnetic bias eld, at least in the eld range where the resonance signal occurs. We show that miniature, magnetically-polarized Nd 2 Fe 14 B particles show promise as magnetic probe tips. However, the interaction between these particles and gradients in the applied bias eld cause an undesirable variation of the cantilever resonance frequency with bias eld. This indicates the importance of ensuring that the applied elds employed in the MRFM experiment be highly uniform.