Fast Switching Of Nano-sized Magnetic Particles

Magnetization reversal of magnetic particles is an important issue in the application of such materials as magnetic data storage, magnetic field sensors and magnetic probes. The stability and fast switching of magnetization are key problems to the magnetic recording media. Periodic arrays of single-domain magnetic dots have attracted much attention dueto their possible applications as high-density magnetic data storage (1 Tb/in~2) andmagnetic sensing devices. In these systems, the dipolar interaction between particles can strongly affect magnetization processes. Especially in small-sized arrays, some interesting phenomena and special properties are found. Therefore, the study of magnetic properties of magnetic nanoparticles is not only for theoretical interests but also valuable for future technological applications.In this thesis, we investigate the magnetization dynamics of magnetic nanoparticles by applying an oscillating bias field instead of a static field, we find that the reversal time becomes much shorter when the switching field is slightly stronger than the effective anisotropy field. A pulsed bias field of a suitably chosen duration in the nanosecond scale can induce a rapid switching, even when the switching field is smaller than the anisotropy field. The dependence of the reversal time on the frequency of an oscillating bias field and the duration of a pulsed bias field are studied. Precessional magnetization reversal of a thin film induced by applying a small oscillating field perpendicular to the easy anisotropy axis is also studied. Compared with the conventional precession switching induced by applying a static field, the transverse oscillating field is more efficient for the magnetization switching for small damping constant α. And the corresponding amplitude of the oscillating field can be an order of magnitude smaller than the anisotropy field when α < 0.01. In high-density magnetic arrays, the dynamic switching of one moment will be obviously affected by the orientations of neighboring moments because of the...