Sensor properties of a robust giant magnetoresistance material system at elevated temperatures

The temperature dependence of the giant magnetoresistance (GMR) ratio, resistance and exchange-biasing field for a spin valve comprising an Ir19Mn81-biased artificial antiferromagnet (AAF) has been studied up to 325 degrees C. Up to 200-250 degrees C the temperature effects are reversible, at higher temperatures gradual irreversible changes are observed, probably due to atomic diffusion. The magnetoresistance effect is even at 200 degrees C still higher than for anisotropic magnetoresistance sensors at room temperature. The resistance of the multilayer shows a maximum around 250 degrees C. We found that this is due to the peculiar behavior of Ir-Mn, which has a negative temperature coefficient of the resistance. This provides a possibility to tune the temperature coefficient for the complete multilayer by varying the thickness of the Ir-Mn layer. The relative decrease of the exchange-biasing field as a function of temperature is much smaller for spin valves with AAF than for conventional spin valves (without AAF). Furthermore, it was demonstrated that the GMR ratio can be increased to 12% at room temperature by using a dual spin valve with two AAFs. (C) 2000 American Institute of Physics. [S0021-8979(00)49008-0].