Magnetic damping losses of tipped cantilevers

In magnetic resonance force microscopy single spin experiments, forces in the attonewton range have to be measured. Non-commercial, soft single crystalline silicon bar cantilevers with a high quality factor and minimized spring constants have to be used, in order to improve the detection sensitivity. In our low temperature force microscope we obtain force sensitivities of the order of 10(-18) N Hz(-1/2) at 10 K (Gysin 2002 Ternperaturerverhalten der Elastizitat und inneren Reibung mikromechanischer Resonatoren, Thesis Basel). Micrometre-sized magnetic particles, which generate a magnetic field of 500 G and magnetic field gradients (dB/dz << 1 G nm(-1)), are attached on ultrasensitive cantilevers. A severe loss in force sensitivity and a frequency shift are observed while exposing a cantilever with a magnetic tip to a homogeneous magnetic field. To minimize the damping losses of the cantilevers with ferromagnetic particles, various magnetic materials (e.g. SmCo5, Nd2Fe14B, and Pr2Fe14B) with different grain and domain sizes are investigated. The lowest magnetic dissipation is observed with SmCo5 and Pr2Fe14B tips. We try to explain the dissipation effect of cantilevers with magnetic tips.