Thermally stable high-moment FeCo/IrMn soft underlayers for perpendicular media

High-moment FeCo/IrMn exchange-coupled multilayer films were demonstrated to have outstanding characteristics as soft underlayers for perpendicular media. However, their thermal stability was not sufficient to maintain the single-domain condition above 75°C. Here, it is reported that an underlayer of β-Ta (200) considerably enhanced the texture in IrMn [111] and FeCo [110] films. An improved structure was found to be glass/Ta(20 nm)/Cu(20 nm)/IrMn(10 nm)/[FeCo(50 nm)/IrMn(10 nm)]₄/FeCo(25 nm), which showed significantly enhanced thermal stability without deterioration in other characteristics. There was no irreversible reduction in the exchange-bias field after the thermal cycle, an increase in the maximum temperature T_max to maintain the single-domain condition of the exchange-bias field greater than the coercivity from 75°C to 150°C, and an increase in the blocking temperature from 175°C to above 250°C. Annealing at 225°C with an orienting field parallel to the pinned direction further enhanced the single-domain condition, resulting in an increase in T_max from 150°C to 220°C.