L10 FePt films with high T capping layer for Heat Assisted Magnetic Recording (HAMR)

The effect of a 1.5 nm thick CoX layer (CAP) of high Curie temperature TC, 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 TRT = 300 K and is shown to be coherent rotations up to a MAG thickness threshold of tcr ∼ 7.5 nm and incoherent, domain-wall mediated, above tcr. The dependence of dHRC/dTT=TC, where HRC is the remanence coercivity, on the MAG thickness indicates tcr is poorly dependent on temperature from TRT up to the MAG TC. The MAG TC distribution, of average 〈TC〉 and standard deviation σTC, is evaluated for both series. The results indicate 〈TC〉 is higher and σTC/〈TC〉 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.