SHIFTED MAGNETIZATION CURVES IN ULTRATHIN CO FILMS ON STEPPED CU(100)

Ultrathin ferromagnetic Alms of Co, grown on a stepped Cu(100) substra te, exhibit, shifted magnetization curves. We calculate the shift fiel d of a film consisting of N planes. Our model includes a four-fold bul k anisotropy k(4), a uniaxial anisotropy k(u) and a magnetic field app lied perpendicularly to the easy magnetisation axis. Even if k(u) is l imited to the outermost plane, a finite shift field h(s) exists, which , for k(u) much less than k(4), is proportional to k(u)/N. This result explains some experimental data.