  Perpendicular exchange bias has been manipulated by changing ferromagnetic
film thickness and spacer layer in Pt/Co/(Pt, Cr)/CoO thin films. The exchange
bias characteristics, blocking temperature, magnetization of thin films
strongly depend on the spacer layer (Pt, Cr) between ferromagnetic and
antiferromagnetic layers. While Pt/Co/Pt/CoO thin films show perpendicular
exchange bias, Pt/Co/Cr/CoO has easy magnetization axis in the film plane. We
have also observed very small hysteretic behavior from the hard axis
magnetization curve of Pt/Co/Cr/CoO film. This can be attributed to
misalignment of the sample or small perpendicular contribution from Pt/Co
bottom interface. We have also investigated the temperature and spacer layer
dependent exchange bias properties of the samples by VSM magnetometry. We
observed higher HEB and HC for the thicker Co layer in the Pt/Co/Pt/CoO sample.
In addition, onset of exchange bias effect starts at much lower temperatures
for Pt/Co/Cr/CoO thin film. This clearly shows that Cr spacer layer not only
removes the perpendicular exchange bias, but also reduces the exchange
interaction between Co and CoO and thus lowers the blocking temperature.
