Perpendicular exchange bias effect in sputter-deposited CoFe/IrMn bilayers

Abstract

CoFe/IrMn bilayers with perpendicular magneti zation for various IrMn layer thicknesses exhibit unusual two-step hysteresis loops with both posi tive and negative loop shifts. Observed at room temperature in the as-grown state, they provide direct evidence of large antiferromagnetic domain formation at the IrMn interface. The e xchange bias field reaches 100mT with an IrMn layer thickness of 4nm after field annealing at 200

C–300

C in 800mT, which is at least three times as large as the coercivity, and may be useful for reference layers of spin-valves or magnetic tunnel junctions with perpendi cular magnetic anisotropy.