NiO films on sapphire as potential antiferromagnetic pinning layers

Epitaxial NiO thin films were grown on single crystal substrates of m-plane ( 101¯0), a-plane ( 1¯1¯20), c-plane (0001), and r-plane ( 11¯02) sapphires by ion beam sputtering of a Ni metal target in a mixed argon and oxygen atmosphere. X-ray measurements indicate that the NiO grows epitaxially on all substrates, with its orientation dependent on the cut of the sapphire substrate. The growth mode is the Stranski–Krastanov mode. (110)-oriented NiO grows on m-plane sapphire, while (111)-oriented NiO films are found on both the a-plane and c-plane sapphire. The orientation of NiO found on r-plane sapphire is found to be surface and temperature dependent but is mainly given by (110)-oriented grains. Thus, thin NiO films on c-plane and a-plane substrates are best suited to serve as antiferromagnetic pinning layers in magneto-electronic devices.