Through detailed experimental studies of the angular dependence of spin wave
excitations in nanocontact-based spin-torque oscillators, we demonstrate that
two distinct spin wave modes can be excited, with different frequency,
threshold currents and frequency tuneability. Using analytical theory and
micromagnetic simulations we identify one mode as an exchange-dominated
propagating spin wave, and the other as a self-localized nonlinear spin wave
bullet. Wavelet-based analysis of the simulations indicates that the apparent
simultaneous excitation of both modes results from rapid mode hopping induced
by the Oersted field.Comment: 5 pages, 3 figure