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

The effect of a 1.5 nm thick CoX layer (CAP) of high Curie temperature T-C, deposited on top of an L1(0) 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) similar to 7.5 nm and incoherent, domain-wall mediated, above t(cr). The dependence of vertical bar dHRC/dT vertical bar(T = TC), 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 a m , is evaluated for both series. The results indicate < T-C > is higher and sigma(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.