Magnetic Nanocrystalline Films Softened by Obliquely Accelerating Iron Nanoclusters

We have generated magnetically ultrasoft thin films composed of iron nanoclusters with diameters of about 20 nm by energetic cluster impact (ECI). The clusters were created in a sputtering-gas-aggregation cluster source with approximately 40% of the particles negatively charged. The charged particles were accelerated onto substrates held at potentials of 0, 5, and 15 kV. The substrates were tilted at an angle of 30deg with respect to the incident beam to generate elliptically shaped clusters and thereby induce shape anisotropy. Visible changes of the film structures were observed for increasing potential with the zero potential samples being black due to the porous nature of soft landed clusters. For the 5 and 15 kV samples, the films take on a metallic sheen due to the increased density. The magnetic properties of the films were measured by SQUID at room temperature. Dramatic softening of the films was observed for samples with applied potentials, in good agreement with the random anisotropy model. The coercivity at zero potential was measured to be 78 Oe. Along the easy axis, the coercivities of the 5 and 15 kV samples were 0.50 and 0.65 Oe and 2.06 and 2.46 Oe for the hard axis, respectively. The coercivities for the axis perpendicular to the substrates were 9.86 and 6.70 Oe. In this experiment, we have demonstrated a novel technique for directly controlling film morphology and thereby ability to custom tailor magnetic characteristics