Structural study by NMR in Co/Cu multilayers at second antiferromagnetic maximum

A Co-59 NMR study has been carried out in a series of Co/Cu multilayer with t(Cu) = 20 Angstrom and 2 Angstrom < t(Cu) < 30 Angstrom. The Co layer is found to have a strained fee structure with hcp stacking faults above 15 Angstrom Co. The lateral size of columnar gains is estimated to be 45 Angstrom. A transformation from continuous to granular Co layer is evidenced below 10 Angstrom Co. Below 3 Angstrom all deposited Co exists in form of a diffused CoCu alloy and Co clusters disappear. These structural changes, together with the decrease of a number of domain walls inferred from the rapid drop of NMR enhancement factor are to be related with the previously observed disappearance of magnetoresistive hysteresis.