Magneto-optical behavior in Co/Pt ultrathin film multilayers

Magneto-optical Kerr effect measurements performed on (0.3 nm Co/x Pt)(15) multilayers with x = 0.3-2.0 nm showed all samples to exhibit strong perpen dicular magnetic anisotropy. Recent work has shown that for compositions ne ar (0.3 nm Co/1.2 nm Pt)(15), both polar Kerr rotation and ellipticity exhi bit bimodal reversals in which the major hysteresis loops have two distinct field-dependent steps due to the contributions of two magnetic phases. To better understand this bimodal magnetization phenomenon, Kerr rotation and ellipticity were determined as a function of radial position from the cente r to the edge of this disk sample. These measurements exhibit a continuous variation from two-step (bimodal) behavior in the center to single-step (un imodal) behavior at the edge. Since these films were deposited via MBE with a heated substrate, it is believed that this phenomenon is related to ther mally induced variations in interface effects such as alloying, abruptness, and morphology. (C) 2000 American Institute of Physics. [S0021-8979(00)453 08-9].