Spin reorientation transition in ultrathin Co film on InP(2x4) reconstructed surface

We have investigated magnetic properties of monolayer (ML)-thickness Co film deposited on InP(2x4) reconstructed surface using in situ surface magneto-optical Kerr effects (SMOKE) measurement system. InP(2x4) reconstructed surface, obtained by several cycles of sputtering-and-annealing process, was confirmed by reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM) measurements. Co film grown on InP(2x4) reconstructed surface shows three distinguishable thickness regions which have different magnetic properties, depending on Co film thickness. In the Co film thickness region smaller than 7 ML, no SMOKE signal was detected. In the thickness region between 8 ML and 15 ML, both longitudinal and polar Kerr hysteresis loops were observed. In the film thickness larger than 16 ML, only longitudinal SMOKE signal without polar signal was detected