Magnetic properties and magnetization reversal in Co/Au multilayers (abstract)

We report studies of magnetic properties in CoX Å/Au60 Å multilayers (X = 5,6,7,8,12,20 Å), which were prepared by sputtering on Si(111) substrates, with emphasis on the magnetization reversal. Magnetization reversal was investigated by measurements of initial magnetization curves, minor loops, coercivity as a function of the maximum field of minor loops, temperature dependence of magnetic properties using Kronmüller’s model, time decay of Kerr rotation angle UK, and the field-sweep speed dependence of coercivity Hc(dHa/dt) at room and/or low temperature. It is found that (1) the thermal activation volumes determined by Hc(dHa/dt) increase from ~ 2.0 × 10–17 to ~ 9.9 × 10–17 cm3 as X varies from 5 to 20 Å, which corresponds to a cylindrical activation volume with ~ 800 Å diameter. (2) A Kronmüller analysis together with the initial magnetization curves, etc., for a Co5 Å/Au60 Å sample at room and low temperature indicates that wall pinning with small pinning sites is the major coercivity mechanism. The interaction between grains was studied with the so-called ΔM method: samples with thin Co layers (X = 5,6,7 Å), which show perpendicular anistropy, exhibit negative ΔM or dipolar interactions, while samples with a thick Co layer (e.g., X = 20 Å), which show in-plane anisotropy, exhibit positive ΔM or ferromagnetic exchange interactions