High-temperature magnetization anomaly in Co/Ag/Si(111) ultrathin films

High-temperature magnetic properties of ultrathin Co/Ag/Si(1 1 1) films wer e studied by surface magneto-optic Kerr effect (SMOKE) in an ultra-high vac uum (UHV) chamber with a background pressure less than 1x10(-10) Torr. A 6 mono-layer (ML) Co layer was deposited on Si(1 1 1) surface with Ag as a bu ffer layer with the thickness being varied between 0 and 5.6 ML. Both polar and longitudinal MOKE (P- and LMOKE) were studied as a function of tempera ture between 300 and 550 K. It is interesting to note that the Kerr intensi ty of LMOKE for Co/Ag/Si(1 1 1) thin film with Ag thickness of 2.8 and 5.6 ML decreases with increasing temperature and vanishes near 475 K; it shows up again in the opposite direction above 475 K before vanishing again at 55 0 K. This was not observed for samples with Ag thickness less than 2.8 ML. This indicates that the Ag buffer layer is playing an important role in the variation of magnetization of Co at high temperature; in other words, stre ss or small Co/Co-Ag clusters formed by the diffusion between AE and Co lay er at high temperature may cause the magnetization anomaly. (C) 2000 Publis hed by Elsevier Science B.V. All rights reserved.