Magnetic properties and microscopic structures of ultrathin Co/√3 × √3 − R30°-Ag/Si(111) films

Combined scanning tunneling microscopy and surface magneto-optic Kerr effect studies were employed to study the relation between magnetic properties and the microscopic interfacial structures of ultrathin Co/√3 × √3 − R30°-Ag/Si(111) films. On the top of √3 × √3 − R30°-Ag/Si(111), pure Co clusters formed without disrupting the √3 × √3 − R30° structure of the Ag buffer layer. The great strain due to the large mismatch between Co and the substrate influenced the nucleation of Co atoms to form large clusters. No magnetic hysteresis in the polar configuration was observed for films thinner than 10 monolayers. The easy axis of magnetization was in the surface plane. Capping √3 × √3 − R30°-Ag on top of the Si(111) surface before the deposition of the Co overlayers can efficiently reduce the nonferromagnetic Co-Si compound to zero thickness. For Co coverage between 2.9 and 4.2 monolayers, a lower Curie temperature was observed in ultrathin films. Due to the existence of a smooth interface between Co and the √3 × √3 − R30°-Ag buffer, the coercivity for Co/√3 × √3 − R30°-Ag/Si(111) is smaller than that for Co/Si(111).