Magnetic Property Enhancement of FePt Films by Zr Underlayering

Structure and magnetic properties of the sputter-prepared FePt (160 nm) and FePt(160 nm)/Zr(10 nm) are studied. The films were deposited at room temperature and followed by a post annealing for magnetic hardening by L10-ordering. Distinct ordering processes are observed. In FePt films, extensive ordering occurs after annealing at Ta=700 ^°C and forms strong (111) texture. Hc increases to 8.5 kOe with a decrease in Mr of about 10%. In contrast, FePt/Zr samples orders at Ta=500 ^°C and results in drastic increase in Hc reaching 12.5 kOe with only 2.7% decrease in Mr. The difference in surface morphology of the two samples suggests that the low temperature ordering is a result of the nucleation promotion by Zr underlayer. The refined grain size strengthens the intergrain coupling resulting in greatly enhanced magnetic properties. The value of (BH)max for the film with Ta=500, 600, and 700 ^°C are 16.8, 20.0, and 19.6 MGOe, respectively. The maximum value is more than 110% higher than that of the FePt film annealed at Ta=700 ^°C (9.5 MGOe).