Magnetization and AC Susceptibility Study of Nb/Ni/Nb Thin Films

A study on the behavior of the magnetization and the ac susceptibility in Nb(40 nm)/Ni(x nm)/Nb(40 nm) thin films was carried out. It was observed that the hysteresis loops of these heterostructures show oscillations of the magnetization in regions of magnetic field where the irreversible reversal of the magnetization of the ferromagnet occurs. This behavior appears to show a coupling between the magnetic fields generated by the vortex in the Nb and the magnetization of the Ni nanograins. The analysis of the real and imaginary components of the ac susceptibility in the tri-layers shows no uniform results in relation to Ni layer thickness. However, the critical temperatures calculated from both components at zero applied field show an oscillation with respect to the Ni layer thickness.