Investigation of spin canting phenomena in perpendicularly exchange biased Pt/Co/Pt/Cr2O3 thin films

Abstract We investigated perpendicular exchange bias and spin canting phenomena in Pt/Co/Pt/Cr 2 O 3 thin films grown on Si (111) substrates. Unusual decrease of perpendicular exchange bias has been observed below 160 K in ultra-thin Co (5 A) and Cr 2 O 3 (0001) exchange coupling system. We also examined the possible deviation of antiferromagnetic spin axis from the c-axis of Cr 2 O 3 (0001) layer by using a thicker Co (50 A) film with a magnetic easy axis lies on the sample plane. The temperature-dependent exchange bias measurements of both samples exhibited that the canting of uncompensated Cr spins at the Cr 2 O 3 surface is responsible for the unusual behavior of perpendicular exchange bias in Co (5 A)/Cr 2 O 3 (0001) ultra-thin film. Furthermore, in-plane angle (φ)-dependent exchange bias experiments with thicker Co (50 A)/Cr 2 O 3 (0001) sample indicated that neither the deviation of antiferromagnetic spin axis from the c-axis of Cr 2 O 3 nor spin–flop transition mechanisms is present in antiferromagnetic Cr 2 O 3 layer. We also found that uncompensated canted Cr spins at the Cr 2 O 3 surface are magnetically disordered (paramagnetic-like) and reduce the exchange coupling between the ferromagnetic Co and antiferromagnetic Cr 2 O 3 (0001) layers. The magnetically disordered uncompensated canted Cr spins negatively affect the perpendicular exchange bias starting from 220 K down to 160 K, and further decrease of temperature dramatically reduces perpendicular exchange bias in Pt/Co/Pt/Cr 2 O 3 thin films.