Dynamic magnetic properties of Ni81Fe19/Al2O3 multilayers

Discontinuous magnetic metal-insulator multilayers of Ni81Fe19 and Al2O3 have been prepared by sequential magnetron sputtering in an UHV chamber. It is found that Ni81Fe19 layers of nominal thickness 8 Å form clusters of quite uniform size having an average diameter of about 24 Å. A layered structure is maintained in the out-of-plane direction, but a random distribution of the metal clusters occurs in plane. These films have magnetic properties that vary strongly with the Al2O3 layer thickness-exhibiting ferromagnetic, spin glass like and superparamagnetic behavior as this layer thickness is increased from 10 via 19 to 31 Å.