Soft magnetic properties of Fe–Zr–B thin films (abstract)

The Fe–Zr–B system has been shown to exhibit superior soft magnetic properties in melt-spun ribbons. These ribbons with composition Fe87Zr7Cu3B3 had very low coercivity (0.02 Oe) and high magnetization (190 emu/g) after crystallization at 540 °C from the amorphous state. We have recently extended these studies to thin films with similar composition. These films were prepared by dc magnetron sputtering from a solid alloy target. Transmission electron microscopy and differential scanning calorimetry were used to study the evolution of the microstructure upon annealing. Magnetic measurements were taken with a hysteresigraph. Unlike the as-spun ribbon samples, the as-sputtered films showed 10 nm crystallities. Selected area diffraction patterns indicated a two phase microstructure, with the bcc phase which gave rise to the soft magnetic properties in the ribbons, coexisting with a second phase leading to degraded soft magnetic properties (Hc=20 Oe and Ms=150 emu/g). Subsequent annealing of the thin film samples enhanced the formation of the second phase and further degraded the soft magnetic properties. Work is currently underway to determine a means of suppressing the formation of the secondary phase while preserving the phase with superior soft properties.