Optimum Laser Exposure for Setting Exchange Bias in Spin Valve Sensors

Abstract

The specific local alignment of the magnetization of a reference layer in spin valves has a rapidly growing significance in the implementation of monolithically integrated sensor devices. The spatial sensitivity of such sensors is defined by the exchange bias effect arising in strongly coupled ferromagnetic (FM) and antiferromagnetic (AFM) heterostructures. The (re-)setting of the orientation of the exchange bias direction can be achieved through local annealing by means of a focused laser beam and subsequent cooling in the presence of a magnetic field. The parameters of such a laser exposure will have a significant influence to the FM/AFM system as well as the remaining layers, playing therefore an important role on the sensing characteristics. In order to analyse this effect, bottom-pinned IrMn / CoFe / Cu / CoFe/ NiFe spin valves are patterned into a meander shape and further annealed using a focused pulsed laser beam. Different processing peak intensities are tested. The analysis of the magnetotransport properties after this exposure shows how strongly the electrical conductivity is affected for higher intensities, as well as the effect of the laser peak intensity on the magnetic coupling between the ferromagnetic electrodes. These changes are discussed as a result of the structural modifications induced by the laser exposure on the spin valve structures.