Effect of Pt underlayer on the coercivity of FePt sputtered film

Magnetic properties of the FePt/Pt bilayers with Pt underlayer were investigated. By introducing the Pt underlayer, coercivity Hc and ordering parameter K of the film were enhanced by about of 50%. After a low-temperature annealing process at only 400 °C, Hc was increased from 6.26 to 9.78 kOe and K was increased from 0.586 to 0.844. Theoretical calculations indicated that there existed a compressive stress in the FePt film. The stress was found to release with the increase in thickness of the Pt underlayer. The increase in lattice parameter aFePt and the decrease in lattice parameter cFePt were closely related to the relaxed compressive stress in the FePt film as the thickness of Pt underlayer was increased. The relaxed compressive stress can account for the enhancement in the ordering parameter and the coercivity of the FePt/Pt bilayer materials.