Surface versus bulk magnetization curves in amorphous GdCo cosputtered in the presence of oxygen

Threshold photoemission and measurement of photoelectron spin polarization are used to investigate surface magnetism while avoiding radiation induced damage. By combining this technique with the measurement of longitudinal Kerr rotation, we show that the magnetic properties of these GdCo films are dominated by metallic Co in a Gd-oxide matrix quite in contrast to findings reported by Togami and Kobayashi [Jpn. J. Appl. Phys. 20, 1457 (1981)]. Mild annealing leaves bulk magnetic properties unchanged but produces dramatic magnetic changes in the surface.