Effects of Intermediate Layers on Chemical Ordering and Hard Magnetic Properties of L1<sub>0</sub> FePt Films

Abstract

The FePt (30 nm)/NiO (2 nm) bilayer films with or without an intermediate layer were deposited on Si substrate at ambient temperature by magnetron sputtering. The films were then post-annealed at 700 °C for 3 min by Rapid Thermal Annealing (RTA) with a high heating ramp rate of 100 °C/sec. The perpendicular coercivity (Hc), in-plane coercivity (Hc//), perpendicular squareness (S) and in-plane squareness (S//) of the film with no intermediate layer are 8.9 kOe, 9.0 kOe, 0.48 and 0.60, respectively. Its chemical ordering is around 0.82. This degrades to 0.62 and 0.48 respectively when Pt and Pd intermediate layers of 5 nm thick are inserted between the FePt and NiO layers. However, when an Ag intermediate layer with a thickness of 5 nm is introduced, the chemical ordering of the film is further increased to 0.91. Its Hc, Hc//, S and S// also increases to 10.2 kOe, 10.6 kOe, 0.62 and 0.68, respectively. The reason for the enhancement in chemical ordering and hard magnetic properties of the FePt film is mainly due to the fact that Ag atoms are immiscible with both Fe and Pt atoms. Instead, Ag tends to segregate at the grain boundary of FePt ; this increases the grain boundary energy, promoting the transformation of soft magnetic fcc FePt into hard magnetic fct L10 FePt films.