Spatiotemporal magnetization reversal dynamics in a Ni(80)Fe(20) microstructure is studied using ps time scale scanning Kerr microscopy. Time domain images reveal a striking change in the reversal associated with the reduction in switching time when a transverse bias field is applied. Magnetization oscillations subsequent to reversal are observed at two resonance frequencies, which sensitively depend on the bias field strength. The oscillation at f = 2 GHz is caused by the damped precession of M, while the lower frequency approximately 0.8 GHz mode is interpreted in terms of domain wall oscillation.

Dynamics of magnetic vortex core switching in nanometer-scale permalloy disk, having a single vortex ground state, was investigated by micromagnetic modeling. When an in-plane magnetic field pulse with an appropriate strength and duration is applied to the vortex structure, additional two vortices, i.e., a circular-and an anti-vortex, are created near the original vortex core. Sequentially, the vortex-antivortex pair annihilates. A spin wave is created at the annihilation point and propagated through the entire element; the relaxed state for the system is the single vortex state with a switched vortex core.

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We report the dynamic hysteresis behavior of epitaxial single ferromagnetic NiFe, Co layers, and NiFe/Cu/Co spin-valve structures investigated as a function of field sweep rate Ḣ (dH/dt) in the range 0.01-270 kOe/sec using the magneto-optic Kerr effect. In situ reflection high-energy electron-diffraction images confirmed that the NiFe, Cu, and Co layers grew epitaxially in the ͑100͒ orientation where the fcc NiFe, Co͗110͘ in-plane directions correspond to the Si͗100͘ directions. For Cu/60 Å NiFe/Cu/Si (H c ϭ5 Oe) and Cu/40 Å Co/Cu/Si (H c ϭ104 Oe) single magnetic layer structures, the hysteresis loop area A is found to follow the scaling relation AϰḢ ␣ with ␣ϳ0.13 and ϳ0.02 at low sweep rates and ϳ0.70 and ϳ0.30 at high sweep rates, respectively. This result indicates that the NiFe and Co layers in the spin-valve structures can be expected to show distinct scaling behavior at high sweep rate. We found that the ''double-switching'' behavior which occurs at low sweep rates transforms to ''single switching'' at ϳ154 kOe/sec and ϳ192 kOe/sec, respectively, for the single and double spin valves due to the different dynamic response of the NiFe and Co layers. Our results provide direct experimental evidence that the magnetic anisotropy strength affects dynamic hysteresis scaling in ultrathin magnetic films, in contrast with the predictions of current theoretical models.

A series of Fe-Co alloys were produced at the atomic scale, onto 15 nm Cu buffer layers, using pulsed-current deposition. The relationship between saturation magnetization, Ms and lattice constant, a has been investigated. The effects of increasing stacking number (bilayer number) on the values of Ms and a have been examined. The alloys showed a maximum room temperature Ms of 240 emu/g at 25 at. % Co. A study to the room temperature magnetic and microstructure analysis revealed that the increase in saturation magnetization strongly correlates with the lattice constant of the Fe-Co alloy.