Domain structure of magnetically micro-patterned PtMn/NiFe exchange bias bilayers

A PtMn/NiFe exchange bias system with an exchange bias field of 180 Oe was magnetically patterned by means of a low fluence focused ion beam. A 1 μm wide stripe pattern with the long axis (1000 μm) oriented parallel to the exchange bias field direction has been irradiated by 2×10¹⁴ Ga⁺/cm². In the irradiated area the coercivity is reduced and the exchange bias field vanishes, while in the nominally nonirradiated region between the irradiated stripes the exchange bias field is reduced to approximately 35 Oe. This reduction is attributed to the magnetic coupling of the irradiated stripes to their intervening nonirradiated regions. Magnetic domain imaging by means of Kerr microscopy and magnetic force microscopy support this interpretation.