Epitaxial Growth and Intrinsic Magnetic Properties of Magnetic Thin Films on Semiconductor Materials

Spin electronics, or spintronics, is an emergent interdisciplinary area whereby the spin degree of freedom in electronic devices is employed. One of the most important topics of spintronics is to develop magnetic/semiconductor hybrid materials for the next generation spin devices such as Spin-FET. This dissertation investigates the magnetic properties of magnetic thin films deposited on semiconductor substrate. Fe and Ni films have been deposited onto GaAs substrate with different substrate treatment. Both single and poly crystalline samples were developed during the process, and the magnetic properties were compared to explore the differences. The origin of a uniaxial magnetic anisotropy (UMA) from the crystal symmetry of the bcc Fe, observed in Fe/GaAs (100) has been investigated.
Another major work for this thesis is the Artemis TR-ARPES (time resolved – angular resolved photoemission spectroscopy) project in Rutherford Appleton Laboratory. Successful MBE growth was achieved for the first time during the Artemis TR-ARPES project, followed by static and time-resolved MOKE, and time-resolved photoemission measurements. Preliminary time-resolved photoemission spectroscopy measurements has been performed on the single crystal Fe samples, which is the world first result in term of the study of the time-dependent valence band structures using direct photoemission technique from a metallic material.
The research finally extended to the CoFeB film on GaAs substrate. The discovery of uniaxial magnetic anisotropy of this amorphous film make it one of the hottest topic in research. XMCD measurements were conducted and the results went through a series of calculations gives an indication of the relation between magnetic moment to the anisotropy. TEM inspections offers a clear look at the interface of the samples.