AVS 47th International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI-TuP

Paper MI-TuP1
Magnetic Properties of Ultrathin Co Films on Si(111)

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: H. Xu, National University of Singapore
Authors: H. Xu, National University of Singapore
A. Wee, National University of Singapore
A. Huan, National University of Singapore
Correspondent: Click to Email
The growth and magnetic behaviour of ultrathin cobalt films on clean(7x7) and Au covered Si(111) were investigated. All experiments including molecular beam epitaxy (MBE) were performed in an ultra-high vacuum (UHV) chamber with a background pressure of 5x10@super-11@ mbar. The Si substrates were introduced via a load-lock and firstly outgassed over night, then the substrates were further cleaned by flashing to 1500K by resistive heating for several seconds. The UHV system was equipped with Auger electron spectroscopy (AES), scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and magneto-optic Kerr effect (MOKE). The growth process was studied using STM and LEED. Magnetic properties were determined with MOKE. It was found that Co nucleates in the initial stage that prefer to grow along the bunched step-edges of the Si substrate(<11-2>), which leads to a strong in-plane uniaxial anisotropy (hard axis along<-110> direction). By introducing Au buffer layers, the tendency for step decoration is reduced, Co grains begin to coalesce on the terrace, so that in-plane uniaxial anisotropy is reduced. However, the magnetic characteristics were improved by the deposition of a Au buffer layer, which partially blocks the silicide reaction between Si and Co. The ferromagnetic inactive layer was found to be decreased to 2.2 ML. By using an higher flashing current, unbunched steps are created on same Si substrate. It is suggested that in this way much more regions for reaction between Si and Co grains arise and a larger amount of CoSi@sub2@ is formed which then deteriorate the magnetic properties of the film in initial layers. Furthermore, in terms of Néel domain wall model and microstructure, different dependencies of coercivity vs. film thickness were discussed.