Straumal, B. B., Mazilkin, A. A., Protasova, S. G., Straumal, P. B., Myatiev, A. A., Schütz, G., et al. (2013). Grain boundaries as the controlling factor for the ferromagnetic behaviour of Co-doped ZnO. Philosophical Magazine, 93(10-12), 1371-1383. doi:10.1080/14786435.2012.736693.