We have investigated the magnetic properties and thermal stability of perpendicular synthetic antiferromagnetic (p-SAF) layers with a [Co/Pt]x/Ru/ [Co/Pt]x structure. A very large exchange coupling field (Hex) of 7.0 kOe was obtained in as-deposited p-SAF structures owing to the large perpendicular magnetic anisotropy of [Co/Pt] and exchange coupling with Ru. We found that a smooth surface of the Ru buffer layer is effective for improving the thermal robustness of [Co/Pt] and demonstrating a large Hex of 2.6 kOe even after annealing at 400°C, which is as high as the integration temperature for Si-based circuits. Such a thermally robust p-SAF layer is promising for developing magnetic sensor devices.
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