Competing exchange interactions in Co-doped ZnO: Departure from the superexchange picture

S. D"Ambrosio,
V. Pashchenko,
J.-M. Mignot,
O. Ignatchik,
A. Savoyant,
Z. Golacki,
K. Grasza,
A. Stepanov

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Physical Review B - Maryland, USA: American Physical Society (APS), 2012, #86


We report the results of a comprehensive study of the exchange interactions in Co-doped ZnO using inelastic neutron scattering, electron paramagnetic resonance, and magnetic property measurements. In particular, we observe an unprecedentedly strong spatial anisotropy of the two nearest-neighbor exchanges, J(1)=-25.6±0.3 K and J(2)=-8.5±0.4 K, along with the distant-neighbor J values of ferromagnetic sign. We argue that the superexchange mechanism alone cannot account for the obtained data and we suggest that an additional mechanism leading to a strong ferromagnetic spin coupling is responsible for these findings. We also discuss the origin of this ferromagnetic mechanism.