Current-driven resonant excitation of magnetic vortex

A magnetic vortex core in a ferromagnetic circular nanodot has a resonance frequency originating from the confinement of the vortex core. By the micromagnetic simulation including the spin-transfer torque, we show that the vortex core can be resonantly excited by an AC (spin-polarized) current through the dot and that the resonance frequency can be tuned by the dot shape. The resistance measurement under the AC current successfully detects the resonance at the frequency consistent with the simulation.Comment: 16 pages, 4 figure

Magnetically Superior and Easy to Handle L10-FePt Nanocrystals

We report a successful synthesis of monodisperse L10-FePt nanocrystals which are not only superior in magnetism but also easy to handle through being dispersible in solvents. Thanks to a thick SiO2-coating, the thermal treatment needed to form the L10 structure can be done even at 900 oC without inducing coalescence and coarsening. The protecting shell was thereafter removed in a specific way that enabled us to recover the L10-FePt nanocrystals in a water-dispersion. The SiO2-coated nanocrystals show a high coercivity of 18.5 kOe at room temperature in spite of their core size of only 6.5 nm in diameter, and the hysteresis loop of the water-dispersed nanocrystals, which were frozen under an external field, was almost rectangular indicating that their magnetic and structural orientation could be attained.Comment: 14 pages, 5 figure