SPIN-REORIENTATION PHASE-TRANSITION IN CO TB AND CO/HO ULTRATHIN FILMS/

Epitaxial buried 16 Angstrom Co/3 Angstrom Tb and 18 Angstrom Co/3 Ang strom Ho films exhibit a continuous (second order) spin reorientation transition (SRT) as a function of temperature near room temperature. T he magnetism and the transition from a perpendicular to an in-plane ma gnetized state with increasing temperature is studied ex situ by SQUID magnetometry, X-ray circular dichroism and by polar magneto-optical K err effect. The uniaxial second-and fourth-order anisotropy constants are determined by recording magnetization loops at lilted angles with respect to the film plane. The second-order uniaxial anisotropy favori ng out-of-plane magnetization decreases almost linearly with increasin g temperature near the SRT, similar to the known bulk behavior of Co. The fourth-order anisotropy constant is nearly constant and positive. From this the tilled angle of the magnetization is calculated as a fun ction of temperature. (C) 1998 Elsevier Science B.V. All rights reserv ed.