Selective realignment of the exchange biased magnetization direction in spintronic layer stacks using continuous and pulsed laser radiation

Abstract

We report on selective realignment of the magnetization direction of the exchange biased ferromagnetic layer in two different spintronic layer stacks using laser radiation. The exchange bias effect occurs in an antiferromagnetic/ferromagnetic bilayer system when cooled in an external magnetic field below the Néel temperature and results in a shift of the ferromagnetic hysteresis loop with increased coercivity. The effect is utilized to pin the magnetization direction of the reference ferromagnetic layer in spin valve systems. We investigated the realignment of the pinned magnetization direction in a spin valve system with in plane exchange bias and in a Co/Pt multilayer with perpendicular exchange bias. The layer stacks were heated above the Néel temperature in a defined lateral area by using rapidly deflected laser radiation. Two different laser assisted annealing techniques were investigated applying either continuous or pulsed laser radiation. During laser annealing, the sample was subjected to an external magnetic field in order to selectively realign the magnetization direction of the pinned ferromagnetic layer. Magnetic structuring was performed by heating narrow single tracks as well as irradiating single pulses. By using a magneto optical sensor in combination with a polarization microscope, the magnetic structures have been visualized. After laser annealing of larger-scaled areas, the exchange bias field strength and the coercive field strength were analyzed using a magneto optical Kerr effect set up (MOKE). The impact of the processing parameters laser peak intensity, laser pulse duration, scan speed (continuous wave) and magnetic field strength on the resulting reversed exchange bias field was evaluated.