We present experimental evidence of sub-GHz spin-transfer oscillations in metallic nano-contacts that are due to the translational motion of a magnetic vortex. The vortex is shown to execute large-amplitude orbital motion outside the contact region. Good agreement with analytical theory and micromagnetics simulations is found.

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We study vortex spin torque oscillators based on magnetic point contacts that operate in zero applied magnetic field. Static and dynamic vortex modes are shown to exist and have distinct electrical signatures. For the oscillatory mode, a spectrally pure slightly asymmetric voltage waveform is observed. It is subject to phase noise as sole fluctuations. The waveforms observed indicate that the vortex orbits outside the point contact region, with a pinned layer magnetization that is static but spatially nonuniform as a result of the current. This nonuniformity results in a reduction in the dc to rf power transduction yield.

We have investigated the generation of spin waves in the free layer of an extended spin-valve structure with a nano-scaled point contact driven by both microwave and direct electric current using Brillouin light scattering microscopy. Simultaneously with the directly excited spin waves, strong nonlinear effects are observed, namely the generation of eigenmodes with integer multiple frequencies (2 f, 3 f, 4 f ) and modes with non-integer factors (0.5 f, 1.5 f ) with respect to the excitation frequency f. The origin of these nonlinear modes is traced back to three magnon scattering processes. The direct current influence on the generation of the fundamental mode at frequency f can be related to the spin-transfer torque, while the efficiency of three-magnon-scattering processes is controlled by the Oersted field as an additional effect of the direct current.PACS numbers: 75.40.Gb; 75.40.Mg; 75.75.+a; Magnetic excitations generated by a high-density electric current in a ferromagnetic nanostructure have attracted growing attention due to the importance of understanding the physical mechanisms responsible for the excitation process. The discovery of the spin transfer torque (STT) effect in 1996 by Slonczewski [1] and Berger [2], i.e. the excitation of the precession of the magnetization in ferromagnetic thin films and nanostructures by a spin polarized direct electric current, has offered a new scheme for spin wave excitation in magnetic nanostructures. In a point contact structure, this torque may excite spin waves whose frequencies are tunable via both current and applied magnetic field [3,4]. The electrical contacts made with diameters less than 100 nm to a continuous spin-valve multilayer stack permit to achieve huge current densities with relatively small applied currents. If the current density is large enough, the STT compensates the natural dissipation processes. This may lead to self-sustained dynamics under and near the point contact such as the formation of nonlinear evanescent bullet modes in the case of in-plane magnetization [5,6]. The impact on spin waves by a microwave current flowing through a point contact was demonstrated [7,8], with possible applications in, e.g., radio-frequency devices for wireless communication.In this letter we report on spin-wave excitations in spin-valve nanocontacts by means of Brillouin light scattering (BLS) microscopy. This technique uses a focused laser spot to probe the spin waves with a spatial resolution of 250 nm and a frequency resolution of up to 50 MHz. A detailed description of the experimental setup can be found in [9,10]. As a result of the very high current densities which can be achieved in a nanocontact, the spin wave system can be driven to amplitudes far beyond the linear regime. Hence, nonlinear processes such as the splitting and the confluence of spin waves can oc- cur. The influence of an additionally applied direct current on these nonlinear processes, either due to STT or the Oersted field, is investigated.The investigated structures consist of an e...