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The vortex state is one of the equilibrium configurations of soft magnetic materials and occurs in thin ferromagnetic square and disk-shaped elements of sub-micrometer size. The vortex state has a specific excitation mode: the in-plane gyration of the vortex structure about its equilibrium position. This mode can be electrically excited by a spin-polarized current. When the gyrating vortex reaches a critical velocity, a switching of the vortex core can occur. We show here how to increase the vortex velocity to reduce the switching current. The vortex core can be switched back by reversing the current direction.

Spin transfer torque oscillators based on magnetic vortex precession can deliver output powers large enough for practical applications. In addition they do not require discrete electronic components, such as capacitors or inductors, to tune the oscillation frequency. At the current stage, this oscillation frequency is still too low and can be increased only by trading off the output power. Here, we present our experimental results on nanocontact oscillators, which are, amongst the spintronic oscillators, those that can deliver the largest power. Based on the analysis of our experimental results, we propose a new device geometry and numerically demonstrate that an increase of the frequency, up to a useful range for practical applications, can be obtained without trading off output power.

Multifunctional, Fe-doped indium tin oxide (ITO) nanostructured films were grown by pulsed laser deposition on sapphire substrates. The films showed low resistivity and n-type conductivity with a carrier density as high as $3\times 10^{21}~{\rm cm}^{-3}$ . A magnetic moment at room temperature larger than those of any iron oxides was measured in films with Fe doping as low as 2%. We ascribe it to the formation of bound polarons. A strong green photoemission at room temperature was observed, which we ascribe to quantum confinement effect. The coexistence of ferromagnetism and luminescence in the visible range makes our films of potential for magneto-optoelectronic applications.