Magnetism of ultrathin Pd₉₉Fe₀₁films grown on niobium

Magnetic properties of ultrathin Pd99Fe01 films grown on niobium films are investigated by magneto-optic visualization, SQUID magnetometry, and Hall-voltage measurements in the temperature range from 3 to 40 K. We show that the films are ferromagnetic at thickness larger than 10 nm. The Curie temperature varies from 2 to 40 K with increase of film thickness to 80 nm. The value of spontaneous magnetization of the Pd99Fe01 depends on the PdFe film thickness. The estimated spin polarization is about 4 per Fe ion, which corresponds to the polarization of the Pd3Fe compound. In contrast to the homogenous bulk material, Pd99Fe01 films consist of ferromagnetic nano-clusters in a paramagnetic host, which is confirmed by characteristic features of the magnetization loops and by the increase of critical current density in the adjacent Nb layer. The size of the clusters is estimated as 10 nm, which is in agreement with the 30% increase of the supercurrent observed in the Nb.