High frequency magneto-acoustics in diluted magnetic semiconductors

Abstract

As fast and as efficient modern hard disk drives have become in the last decades, the need for increasing data processing speeds is greater than ever. The speed up of conventional techniques relying on the application of magnetic fields for magnetic bit writing is limited by the ability to generate spatially well located magnetic fields on the picosecond time scale. New techniques have to be developed to increase device performances that do not rely on the need of external magnetic fields. A novel, non-magnetic and all-optical approach is presented in this thesis. Ultrafast strain pulses, generated by the technique of picosecond acoustics, are interacting with the magnetic anisotropy of a thin layer of the ferromagnetic semiconductor (Ga,Mn)As. The strain pulse changes the magnetic anisotropy and a fast response on the time scale of 50 ps can be observed by utilizing the magneto-optic Kerr effect in a pump-probe scheme. By the application of ultrashort shear strain pulses magnetization precession amplitudes exceeding 10 % of the saturation magnetization can be obtained and appropriate magnetic field tuning allows for precession frequencies beyond 50 GHz. The technique allows for real magnetic switching in principle, but the unavailability of a laser source with strong enough peak intensity prevented the realization in the experiment.