Study on microstructural and magnetic properties of ultrathin Co films on InP (2x4) substrate

Abstract

Since L. Datta and B. Dass had proposed a spinelectronic analog of the electro-optic light modulator. this system open the way to what was later called spintronics. The Ferromagnet/semiconductor is a representative system in spintronics and the growth of ferromagnetic films on semiconductors offers the opportunity for many new technological applications such as magnetic tunnel junction and spin valve transistor etc. I n this study, we have investigated magnetic properties of Co films on InP (2x4) reconstruction surface. Experiments are mainly divided into two processes. One is to form flat InP (2x4) reconstruction surface. The other is to observe the magnetic properties of Co on InP (2x4) reconstruction surface by in-situ SMOKE measurements. In order to form InP reconstruction surface, we sputtered and annealed. Therfore we obtain InP (2x4) reconstruction surface by sputterig the sample at the pressure of $2x10^{-7}$ Torr, and anneling at 400℃ for 20~30 minutes over 8 times repeatedly. We confirmed these results by RHEED and STM measurements. As the next stage, we grew Co films on InP (2x4) reconstruction surface at room temperature and observed magnetic properties of Co films through in-situ SMOKE measurements. As a result we observed three distinguishable regions with different magnetic properties. First is region I that there is no signal due to magnetic dead layer or superparamagnetic layer (2 ML ~ 7 ML). Second is region II that Kerr signals in both longitudinal and polar measurements are not detected (8 ML ~ 15 ML). In this region, square loops with low coercivity appear in longitudinal SMOKE measurements. Third is region III that polar Kerr signal is not detected, and coercivity increase abruptly in longitudinal measurement (16 ML ~). Especially, longitudinal loop shows a step at 16 ML. One possibility is the existence of anisotropy in a specific direction different from applied field direction. For verification, we observed SMOKE signals in...