Chemical Ordering of Sputtered FePt / h-BN Granular Media Using RF Substrate Bias

Recently hexagonal-BN (h-BN) / L1 0 -FePt granular media has been proposed as an ideal candidate for next generation heat assisted magnetic recording (HAMR) media. The formation of crystalline h-BN at the FePt grain boundaries has resulted in significant enhancements to the sputtered media's microstructural and magnetic properties. While it has been shown that high temperature and RF substrate bias are necessary to achieve highly crystalline h-BN at the grain boundaries, limited discussion has been given to the broader impact of substrate bias on the chemical ordering of FePt within this system. To further evaluate the influence of RF substrate bias on sputtered FePt / h-BN granular media we have prepared several samples using different RF bias powers, 3 W / -21 V DC to 8 W / -70 V DC , on Corning NXT TM glass substrates. It was observed that the L1 0 chemical ordering of the system decreased with increased substrate bias over the above range. This behavior was confirmed in the magnetization data which also reflected a reduction of the out of plane coercivity from 32 kOe to 10 kOe for the -21 V DC and -70 V DC substrate bias samples respectively. Additionally, energy dispersive spectroscopy (EDX) was used to probe the composition of the deposited h-BN / FePt films. This revealed a reduction in the Fe at% observed for all samples deposited with increased substrate bias. Relevant structural, microstructural, magnetic, and compositional data are presented below.