Abstract
The fine control of the exchange coupling strength and blocking temperature ofexchange bias systems is an important requirement for the development of magnetoresistive sensors with two pinned electrodes. In this paper, we successfully tune these parameters in top- and bottom-pinned systems, comprising 5 nm thick Co40Fe40B20 and 6.5 nm thick Ir22Mn78 films. By inserting Ru impurities at different concentrations in the Ir22Mn78 layer, blocking temperatures ranging from 220 °C to 100 °C and exchange bias fields from 200 Oe to 60 Oe are obtained. This method is then applied to the fabrication of sensors based on magnetic tunneling junctions consisting of a pinned synthetic antiferromagnet reference layer and a top-pinned sensing layer. This work paves the way towards the development of new sensors with finely tuned magnetic anisotropies.
Highlights
Magnetic sensors have been applied to different fields [1,2], ranging from automotive applications [3,4] to biology [5]
In all cases the exchange bias field diminishes with the temperature, due to the fact that the expected, in all cases the exchange bias field diminishes with the temperature, due to the fact that the fraction of IrMn grains contributing to the pinning of the CoFeB layer decreases with temperature
In polycrystalline films like sputtered IrMn, the distribution of the grain sizes leads to a in polycrystalline films like sputtered IrMn, the distribution of the grain sizes leads to a distribution in the blocking temperatures of the system [27]
Summary
Magnetic sensors have been applied to different fields [1,2], ranging from automotive applications [3,4] to biology [5]. Magnetoresistive sensors in combination with magnetic nanoparticles have been employed for detecting synthetic [6,7,8] and natural DNA and proteins [9]. In all these applications, the sensitivity of the experiment is determined by the sensor performance, and by different factors such as the selectivity and specificity of the biological probes, the methods employed for sample preparation, the binding of the target in the biological sample, the labelling and the detection scheme [6,10]. Spin valve (SV) and MgO-barrier magnetic tunneling junctions (MTJs) have been intensively investigated for this purpose [11,12,13]
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