Optical spin injection and XMCD in ultrathin magnetic films deposited on GaAs

The primary aim of this work is to study optically excited spin injection over a ferromagnetic metal-semiconductor Schottky barrier. A novel experimental approach has been introduced which enables the determination of the sign in the magnetic asymmetry of the photocurrent, hence the sign in the spin polarisation.The magnetic ultrathin films are grown on GaAs substrates using an e-beam evaporation technique in an ultrahigh vacuum system. The elemental and chemical characterisation of the Fe/GaAs samples has been conducted using x-ray absorption spectroscopy (XAS) whilst x-ray magnetic circular dichroism (XMCD) is utilised to obtain the magnetic information. The temperature-dependent magnetic properties of the samples are examined and the orbital, spin moments are estimated with classical optical sum rules. The magneto-optical Kerr effect (MOKE) is also employed to characterise the magnetic properties of ultrathin Ni, Fe films on GaAs substrates.The study of the spin injection processes is carried out with photoexcitation of electrons using circularly polarised light. Pure left and right circularly polarised light obtained using a Soleil-Babinet compensator plays a key role in the study of the spin injection processes. The influence of the magnetization of the ultra thin magnetic films on the chirality-dependent photocurrents is attributed to the effect of the spin-polarised density of states of the ferromagnetic films. Interestingly, under appropriate experimental conditions, a negative magnetic asymmetry in the photocurrent can be observed with Ni films, which are known to have a negative spin polarization for the electrons near the Fermi level. The study focuses on the use of a non-normal incidence experimental geometry in which various experimental factors are carefully explored. The influences of photon energy on the magnetic asymmetry in photocurrent have been examined providing a better understanding of the spin injection process