Cheng Hsun Tony Chang

Interaction transfer of silicon atoms forming Co silicide for Co/ 3×3R30°-Ag/Si(111) and related magnetic properties

Combined scanning tunneling microscopy, Auger electron spectroscopy, and surface magneto-optic Kerr effect studies were employed to study the microscopic structures and magnetic properties for ultrathin Co/ 3×3R30°-Ag/Si(111). As the annealing temperature increases, the upward diffusion of Si atoms and formation of Co silicides occurs at temperature above 400 K. Below 600 K, the 3×3R30°-Ag/Si(111) surface structure persists. We propose an interaction transferring mechanism of Si atoms across the 3×3R30°-Ag layer. The upward transferred Si atoms react with Co atoms to form Co silicide. The step height across the edge of the island, a separation of 0.75 nm from the analysis of the 2 × 2 structure, and the calculations of the normalized Auger signal serve as strong evidences for the formation of CoSi2 at the interface. The interaction transferring mechanism for Si atoms enhances the possibility of interactions between Co and Si atoms. The smoothness of the surface is advantage for that the easy axis of magne...

Variation of blocking temperatures for exchange biased CoO/Co/Ge(100) films

Variations of the blocking temperature and related structures for CoO/Co/Ge(100) films are investigated by employing reflection high energy electron diffraction, Auger electron spectroscopy, and surface magneto-optic Kerr effect measurements. By increasing the CoO thickness, the blocking temperature is smaller than the Neel temperature of CoO. The monotonous increase of the blocking temperature is mainly attributed to the increasing thermal stability of the antiferromagnetic grains by way of increasing the antiferromagnetic thickness. The deviation of the blocking temperature from the linear relation and the full widths at half maximum of the diffraction spots show a similar trend. The minimums appear around 25 monolayer of CoO and are related to the formation of larger grains.

Compositions and Magnetic Properties of CoO/Co/Ge(111) Films

On the top of Co/Ge(111) films, cobalt oxides are prepared by evaporating Co atoms in an oxygen atmosphere. Depth profiling measurements show a layered structure of a pure Co layer covered by a CoO overlayer. As the CoO thickness increases, the Auger intensity ratio of O KL2L2 and Co L3M45M45 Auger signals increases until reaching a saturated value which shows a CoO layer with a concentration ratio of Co and O close to 1:1. After introduction of CoO overlayers on Co/Ge(111), hysteresis occurs in the longitudinal configuration and CoO/Co/Ge(111) exhibits in-plane anisotropy. A slight reduction of the Kerr intensity occurs due to the oxidation of cobalt at the CoO/Co interface while an enhanced coercive force is observed owing to the imperfection introduced by oxygen to impede the magnetization reversal. Under conditions of cooling in a magnetic field, exchange bias field increases as the sample temperature decreases resulting from the formation of an antiferromagnetic/ferromagnetic interface.

Tuning coercive force by adjusting electric potential in solution processed Co/Pt(111) and the mechanism involved

A combination of a solution process and the control of the electric potential for magnetism represents a new approach to operating spintronic devices with a highly controlled efficiency and lower power consumption with reduced production cost. As a paradigmatic example, we investigated Co/Pt(111) in the Bloch-wall regime. The depression in coercive force was detected by applying a negative electric potential in an electrolytic solution. The reversible control of coercive force by varying the electric potential within few hundred millivolts is demonstrated. By changing the electric potential in ferromagnetic layers with smaller thicknesses, the efficiency for controlling the tunable coercive force becomes higher. Assuming that the pinning domains are independent of the applied electric potential, an electric potential tuning-magnetic anisotropy energy model was derived and provided insights into our knowledge of the relation between the electric potential tuning coercive force and the thickness of the ferromagnetic layer. Based on the fact that the coercive force can be tuned by changing the electric potential using a solution process, we developed a novel concept of electric-potential-tuned magnetic recording, resulting in a stable recording media with a high degree of writing ability.