Effect of thermal annealing and ion radiation on the coercivity of amorphous Gd--Co films

Ferrimagnetic amorphous Gd–Co films deposited by rf sputtering with uniaxial perpendicular anisotropy were annealed at about 200 °C with or without a magnetic field of 3 kOe applied perpendicularly to the film plane. Data taken using the polar Kerr magneto-optic effect show a significant decrease in the value of the wall-motion coercivity Hc. A reduction of Hc by an order of magnitude was generally attained in films having compositions in the vicinity of the magnetic compensation point. Similar results were obtained in a film irradiated with 2.5-MeV argon ions. These data are discussed in terms of fluctuations in various parameters contributing to the resultant coercivity. The results indicate that the fluctuations in the exchange stiffness constant dominate over the others and, consequently, are most affected by the postdeposition treatments. The results for the ion-irradiated film suggest that the origin of the uniaxial anisotropy is due to pair ordering of Co atoms.