Micromagnetic study of full widths at half maximum in spin-transfer-driven self-oscillations of individual nanomagnets

A full micromagnetic study of the spin-transfer-driven self-oscillations of individual ellipsoidal PyCu nanomagnets as small as 30×90×5.5 nm3 is presented. The magnetic parameters have been computed by fitting static magnetoresistance measurements. The main mode found in the experiments by Sankey [Phys. Rev. Lett. 96, 227601 (2006)] is analyzed. The full width at half maximum is calculated without taking into account the effect of thermal activation. The full width is found to decrease from 6.5 to 3.3 MHz when increasing the current in the self-oscillation region. These narrow widths are mainly produced by the nonuniformities of the magnetization and since they are computed at zero temperature mark a limit for the spectral purity of the self-oscillations in those nanomagnets.