Effect of crystal orientation of Cr_2O_3 layer on magnetic properties of ferromagnetic/Cr_2O_3 interface

摘要

Magnetoelectric materials has been intensively investigated to realize electric controlled spintronic device such as magnetoelectric random access memory (MERAM. Magnetoelectric antiferromagnet Cr_2O_3 is the most powerful candidate for the application, due to the high Neel temperature T_N-307 K. For the electrical control of magnetization of ferromagnetic layer, exchange coupling between Cr_2O_3 and ferromagnetic layers is essential. In the past, we reported high exchange bias (H_(ex)) at ferromagnetic layer/Cr_2O_3 layer interface. The Cr_2O_3 layer was fabricated by room temperature sputtering with sequential high temperature annealing in high O_2 flow. The Cr_2O_3 layer was quite different form that previously reported; the Cr_2O_3 layer was not epitaxially grown on c-Al_2O_3 substrate, and oblique R-planes were self-organized on the surface of each grain. From the fact that uncompensated Cr spins are not only on C-plane, but also R-plane of Cr_2O_3, we concluded the oblique R-planes are the origin of the H_(ex). The crystal orientation of Cr_2O_3 layer after annealing is strongly affected by sputtering conditions before annealing. Recently, we found that c-axis oriented Cr_2O_3 was possible to fabricate by same annealing conditions, if we change the sputtering atmosphere. In this study, we tried to clarify the difference in magnetic properties between Cr_2O_3 with oblique R-plane and c-axis oriented Cr_2O_3.