SPIN-REORIENTATION TRANSITION IN ULTRATHIN TB CO FILMS/

A series of terbium (0-6 Angstrom)/Co (16 Angstrom) films deposited on Ru(0001) under ultrahigh vacuum conditions and covered by 40 Angstrom Ru have been investigated ex situ by means of the magneto-optic Kerr effect (MOKE). Combined polar and longitudinal loops (dc-MOKE) show a reversible rotation of the remanent magnetization from out-of-plane to in-plane with increasing temperature. The reorientation is continuous and occurs without loss of long-range order. It is discussed in terms of the competition between dipolar demagnetization energy and second- and fourth-order magnetocrystalline anisotropy contributions. The swi tching of the easy axis of magnetization is confirmed by the susceptib ility peak observed in a 10 Oe oscillating field (ac-MOKE) applied per pendicular to the film plane. The transition temperature varies from 3 23 K (1 Angstrom Tb) to 277 K (6 Angstrom Tb).