Numerical study on the self-modulated solitons excited in a spin-torque nanocontact oscillator

Among the different studies on spin-torque nanocontact oscillators (STNOs) [1], it was proved that such devices can work as nonlinear modulators of both frequency and amplitude. This occurs if they are subject to the simultaneous action of a direct and an alternative current, the latter acting as a modulating signal [2]. Nonetheless, more recently, self-modulation dynamics were observed in an STNO where the thin free layer had a strong perpendicular magnetic anisotropy (PMA) [3-4]. In this case, typical frequency spectra with lateral bands were found out, associated to the excitation of a deformed high-frequency droplet (bubble-like) soliton [3-6]. In this work we show a systematic numerical analysis on STNOs with PMA, through the variation of some parameters in the micromagnetic framework. More in detail, we study a device composed by a metallic nano-contact with a radius of 30 nm on the top of a Co/Cu/Co-[Ni/Co]x4 orthogonal thin layer with a squared section.