Synthetic Antiferromagnetic Soft Underlayers for Perpendicular Recording Media

Abstract

Synthetic antiferromagnetically coupled films have been studied for soft underlayers for perpendicular media. Initially, FeCo bilayers were prepared by dc magnetron sputtering with a structure of glass-Ru(2.5 nm)-FeCo(t/sub F/)-Ru(t/sub Ru/)-FeCo(t/sub F/)-Ru (10 nm), where t/sub F/ was varied from 5 to 200 nm and t/sub Ru/ from 0.2 to 1.4 nm. The antiferromagnetic coupling showed a maximum at t/sub Ru/=0.6-1.0 nm as expected, depending on t/sub F/. However, the surface coupling energy J/sub AF/ decreased very rapidly with t/sub F/ from 2.8 erg/cm/sup 2/ at t/sub F/=5 nm to 0.6erg/cm/sup 2/ at t/sub F/=10 nm. A structure of glass-Ru(2.5 nm)-FeCo(50 nm)-Ru(1.0 nm)-FeCo(55 nm)-Ru (10 nm) showed nearly zero remanence and very well separated hysteresis segments at /spl plusmn/30 Oe along the FeCo easy axis and a single narrow hysteresis loop with coercivity of 3.5 Oe along the hard axis. These characteristics were thermally stable up to at least 200/spl deg/C, which is superior to IrMn exchange-biased systems. Further optimization was achieved with a trilayer structure of glass-Ru(2.5 nm)-FeCo(25 nm)-Ru(1.0nm)-FeCo(45nm)-Ru(1.0 nm)-FeCo(25 nm)-Ru (10 nm).