Effects of temperature on intergranular exchange coupling in L1 FePt thin films

Abstract

The effects of temperature on intergranular exchange coupling for FePt:X:FePt (X = TaOx, SiOx, Cr) sputtered thin film stacks were investigated. In-plane FePt layers separated by a thin layer of segregant were used as an experimental model for the intergranular region in perpendicular recording media. Magnetic hysteresis was measured for varying segregant thicknesses (0.5 nm–1.5 nm) at varying temperatures (300 K–700 K). Exchange coupling energies were calculated using the reversal field, saturation magnetization, and coercivity. The intergranular exchange coupling energy was observed to be well-behaved, decreasing linearly with increasing temperature to 600 K. TaOx resulted in the lowest exchange coupling energy at any given temperature, while SiOx and Cr showed similar decoupling capabilities. At 600 K and beyond, antiferromagnetic behavior was observed. Exchange coupling was found to be negligible at operating temperatures above 600 K even with as little as 0.5 nm of TaOx segregant or 1 nm of SiOx segregant.