AVS 51st International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI-TuP

Paper MI-TuP1
Comparative Studies of Magnetic Phases of the Interfacial Layers for Co/Ge(100) and Co/Ge(111) Films

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: J.S. Tsay, National Chung Cheng University, Taiwan
Authors: J.S. Tsay, National Chung Cheng University, Taiwan
C.W. Su, Academia Sinica, Taiwan
C.H. Hwang, Tunghai University, Taiwan
Y.D. Yao, Academia Sinica, Taiwan
Correspondent: Click to Email
Magnetic phases of the interfacial layers were comparatively investigated for Co/Ge(100) and Co/Ge(111) films thinner than 13 monolayers using surface magneto-optic Kerr effect technique. Co/Ge(100) films show nonferromagnetic behavior up to 12 monolayers at 300 K. After systematic investigations of the magnetic properties upon cryogenic treatments, magnetic phase diagram of the Co/Ge(100) films was established. The boundary between nonferromagnetic and ferromagnetic phases was experimentally determined to be from below 150 K to above 300 K as the cobalt thickness increases from 9 to 14 monolayers. This behavior is consistent with the thickness-dependent scaling law of Curie temperature for a thin film system. As comparing to Co/Ge(111) system, this boundary shifts to higher Co thickness side. Due to the difference of the electronegativities for Co and Ge atoms, Co LMM Auger line shifts to a higher kinetic energy as the Co thickness increases. This gives the spectroscopic evidence of the formation of interfacial compounds. Co/Ge(100) exhibit a diffused 2x1 diffraction pattern within the first monolayer thickness followed by a diffused background for thicker films as observed using low-energy electron diffraction technique. Ordered structure up to several monolayers were observed for Co/Ge(111) films as deposited at 300 K. In additional, the critical exponent @beta@ï? in the power law relationship of magnetization for Co/Ge(100) films is about 0.38 that lies close to the value expected by three-dimensional Heisenberg model, while the critical exponent of Co/Ge(111) is close to the value of two-dimensional XY model. These experimental evidences show that the structure of Co/Ge(100) interfacial layers is in a much disordered state. This causes a three-dimensional stacking of subsequently deposited Co atoms and furthermore the different magnetic transition behavior of Co/Ge(100) and Co/Ge(111) films.