Magneto-optic Kerr effect study of a two-step reorientation transition of an ultrathin magnetic film

The magnetic reorientation transition for ultrathin Fe films on Gd is studi ed. At low temperatures, the films are magnetized in plane and at intermedi ate temperatures they undergo a reorientation to out of plane. The reorient ation is attributed to the reducing magnetization of Gd as it approaches it s Curie temperature and the perpendicular magnetic anisotropy at the Fe sur face. Detailed measurements of the reorientation were made in situ using th e magneto-optic Kerr effect (MOKE). The first step, at low temperature, is a continuous, reversible reorientation of the surface moment from in plane to canted out of plane; a corresponding peak in the susceptibility identifi es it as a second-order phase transition. The second step is a discontinuou s, irreversible rotation from this canted direction to perpendicular to the film plane; thermal hysteresis of the magnetization identifies it as a fir st-order phase transition. The MOKE thermal hysteresis loop shows that the Gd surface region participates in the first-order phase transition. (C) 200 0 American Institute of Physics. [S0021-8979(00)31508-0].