Nanocrystalline high coercivity PrCo//Cr thin films: Potential high density magnetic recording media

Abstract

PrCo thin films with a Cr underlayer (PrCo//Cr) have been prepared by dc magnetron sputtering. The as-deposited PrCo films with a Cr underlayer of 80 nm have coercivity values of about 300 to 400 Oe but after annealing at 400°C for 20 min a large enhancement in the coercivity is observed. The coercivity of the PrCo films after annealing at 400°C varies from 2 kOe to as high as 8 kOe depending on the film thickness and deposition conditions. The as-deposited PrCo//Cr films have a mostly amorphous PrCo layer but after annealing at 400°C the PrCo layer is nearly 100% crystalline with a grain size of about 10 nm as revealed by the high resolution TEM micrographs. The coercivity of the films depends strongly on the Ar pressure during sputtering of the PrCo layer, while the Ar pressure for the Cr underlayer does not significantly change the coercivity of the films. The Cr underlayer thickness was varied from 10 to 160 nm and only a slight change in coercivity was observed. The magnetic switching volume was estimated by the dependence of apparent coercivity on the sweep rate of the magnetic field and also through magnetic viscosity and remanence measurements. The measured switching volume is of the order of 1 to 1.5 × 10 −18 cm 3.