Hamadeh, A. et al. ; © 2014 American Physical Society. It is demonstrated that the threshold current for damping compensation can be reached in a 5 μm diameter YIG(20 nm)|Pt(7 nm) disk. The demonstration rests upon the measurement of the ferromagnetic resonance linewidth as a function of Idc using a magnetic resonance force microscope (MRFM). It is shown that the magnetic losses of spin-wave modes existing in the magnetic insulator can be reduced or enhanced by at least a factor of 5 depending on the polarity and intensity of an in-plane dc current Idc flowing through the adjacent normal metal with strong spin-orbit interaction. Complete compensation of the damping of the fundamental mode by spin-orbit torque is reached for a current density of ∼3×1011 A⋅m−2, in agreement with theoretical predictions. At this critical threshold the MRFM detects a small change of static magnetization, a behavior consistent with the onset of an auto-oscillation regime. ; This research was supported by the French Grants Trinidad (ASTRID 2012 program), by the RTRA Triangle de la Physique grant Spinoscopy, and by the Deutsche Forschungsgemeinschaft. S. O. D. and V. V. N. acknowledges respectively support from the Russian programs Megagrant No. 2013-220-04-329 and competitive growth of KFU. ; Peer Reviewed