We report a high-resolution experimental detection of the resonant behavior of magnetic vortices confined in small disk-shaped ferromagnetic dots. The samples are magnetically soft FeNi disks of diameter 1.1 and 2.2 µm, and thickness 20 and 40 nm patterned via electron beam lithography onto microwave co-planar waveguides. The vortex excitation spectra were probed by a vector network analyzer operating in reflection mode, which records the derivative of the real and the imaginary impedance as a function of frequency. The spectra show well-defined resonance peaks in magnetic fields smaller than the characteristic vortex annihilation field.Resonances at 162 and 272 MHz were detected for 2.2 and 1.1 µm disks with thickness 40 nm, respectively. A resonance peak at 83 MHz was detected for 20-nm thick, 2-µm diameter disks.The resonance frequencies exhibit weak field dependence, and scale as a function of the dot geometrical aspect ratio. The measured frequencies are well described by micromagnetic and analytical calculations that rely only on known properties of the dots (such as the dot diameter, thickness, saturation magnetization, and exchange stiffness constant) without any adjustable parameters. We find that the observed resonance originates from the translational motion of the magnetic vortex core.

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ExperimentalCharacterization: The UV-visible spectra were recorded on a Shimadzu 3101 spectrophotometer. Dynamic light scattering studies were carried out using a Horiba LB-550 instrument. Transmission electron micrographs of the clusters were recorded by applying a drop of the sample to a carbon-coated copper grid (JEOL JEM-200CX). AFM measurements were obtained using a Digital Nanoscope III in the tapping mode.Photoelectrochemical Measurements: The photoelectrochemical measurements were performed in a one-compartment Pyrex UV cell with a standard three electrode arrangement consisting of a working electrode, a Pt wire counter electrode, and a Ag/AgNO 3 reference electrode (0.5 M LiI and 0.01 M I 2 in acetonitrile as the electrolyte). Photocurrent measurements were made with an ALS 630A electrochemical analyzer. Monochromatic light obtained by passing light from a 500 W xenon lamp (Ushio XB-50101AA-A) through a monochromator (Ritsu MC-10N) was used for excitation.

The rich internal degrees of freedom of magnetic domain walls make them an attractive complement to electron charge for exploring new concepts of storage, transport and processing of information. Here we use the tunable internal structure of a domain wall in a perpendicularly magnetized GaMnAsP/GaAs ferromagnetic semiconductor and demonstrate devices in which piezoelectrically controlled magnetic anisotropy yields up to 500% mobility variations for an electrical-current-driven domain wall. We observe current-induced domain wall motion over a wide range of current-pulse amplitudes and report a direct observation and the piezoelectric control of the Walker breakdown separating two regimes with different mobilities. Our work demonstrates that in spin-orbit-coupled ferromagnets with weak extrinsic domain wall pinning, the piezoelectric control allows one to experimentally assess the upper and lower boundaries of the characteristic ratio of adiabatic and non-adiabatic spin-transfer torques in the current-driven domain wall motion.