R&D: L10 FePt Films With High TC Capping Layer for HAMR

Journal of Magnetism and Magnetic Materials has published an article written by C.Papusoi, T. Le, P.-O. Jubert, D. Oswald, B. Ozdol, D.Tripathy, P. Dorsey, M. Desai, Western Digital, 1710 Automation Parkway, San Jose, CA 95131, USA.

Abstract: “The effect of a 1.5 nm thick CoX layer (CAP) of high Curie temperature T_C, deposited on top of an L1₀ Fe₅₀Pt₅₀ layer (MAG) on the properties of the MAG/CAP bilayer is investigated. Two series of samples are studied: “w/o CAP” are single MAG layers of thickness in the 3.8–10.5 nm range and “w/CAP” are MAG/CAP bilayers of MAG thickness in the 3.8–10.5 nm range and 1.5 nm CAP. For both series, magnetization reversal is investigated at T_RT = 300 K and is shown to be coherent rotations up to a MAG thickness threshold of t_cr ∼ 7.5 nm and incoherent, domain-wall mediated, above t_cr. The dependence of , where H_RC is the remanence coercivity, on the MAG thickness indicates t_cr is poorly dependent on temperature from T_RT up to the MAG T_C. The MAG T_C distribution, of average 〈T_C〉 and standard deviation σ_TC, is evaluated for both series. The results indicate 〈T_C〉 is higher and σ_TC/〈T_C〉 is lower w/CAP than w/o, particularly at low MAG thicknesses. This behavior is interpreted as a consequence of spin exchange hardening in the MAG layer in the proximity of the MAG/CAP interface. For the w/CAP case, the saturation field of the Thermoremanent magnetization exhibits a non-motononic dependence on the MAG thickness, displaying a maximum. This behavior indicates the CAP assists the applied field to set the MAG layer magnetization during a HAMR process, the assist effect becoming more efficient the lower is the MAG thickness.“