Atomic layer stacking structure and negative uniaxial magnetocrystalline anisotropy of Co100−xIrx sputtered films

• Published in: Journal of the Magnetics Society of Japan 2013/05/01, Vol.37(3-2), pp.183-189
• Main Authors: Nozawa, N., Saito, S., Kimura, T., Shibuya, K., Hoshino, K., Hinata, S., Takahashi, M.
• Format: Article
• Language: eng ; jpn
• Subjects: CoIr sputtered film; High−angle annular dark−field; Negative uniaxial magnetocrystalline anisotropy; Stacking faults; Superlattice line
• ISSN: 1882-2924; 1882-2932
• DOI: 10.3379/msjmag.1305R005

The negative uniaxial magnetocrystalline anisotropy (Ku) was evaluated for various compositions of Co100−xIrx thin films with respect to the atomic layer stacking structure. Pure Co film fabricated at a substrate temperature (Tsub) of 600 ℃ was found to have a positive Ku of 6.1×106 erg/cm3. With increasing x, the sign of Ku changed from positive to negative, and the negative Ku took a maximum value of −9.6×106 erg/cm3 at around x = 20 at. % for films fabricated at Tsub = 600 ℃. Adding more Ir decreased the absolute value of the negative Ku which became 0 over x = 50 at. %. X−ray diffraction analysis and scanning transmission electron microscopy revealed that the atomic layer stacking structure of the Co100−xIrx films changed from −A−B−A−B− (hcp) to −A−B−C−A−B−C− (fcc) stacking with increasing Ir content. Moreover, Co80Ir20 grains were revealed to consist of 2 kinds of randomly located composition−modulated atomic layers, nearly pure−Co and pure−Ir layers, while Co and Co50Ir50 had disordered structures. In this paper, a new perspective on the atomic layered structure with superlattice diffraction, which is different from the conventional “ordered structure”, is discussed.