Reactive sputtering synthesis of Co-CoO/Ag nanogranular and multilayer films containing core-shell particles

We present magnetic characterization of two series of samples grown by reactive sputtering of Co and Ag: (i) thin films obtained by cosputtering of these metals at different oxygen pressures, and (ii) Co∕Ag multilayer films deposited with fixed Co layer thickness (1.1nm) and oxygen pressure (2×10−5mbar), and varying Ag layer thickness tAg. For certain preparation conditions the samples obtained with both synthesis methods consist of a dispersion of core-shell Co–CoO nanoparticles embedded in a Ag matrix. Regarding series (i), it is remarkable that the interesting core-shell/matrix structure, suggested by exchange-bias and giant magnetoresistance properties, could be achieved using the simple one-step technique of reactive cosputtering. In series (ii), the exchange-bias and coercivity fields strongly depend on the spacer layer thickness for tAg<4nm, and then become roughly thickness independent. A discontinuous-continuous transition in the silver layers with increasing tAg, similar to that observed in a pr...