Indication of antiferromagnetic interaction between paramagnetic Co ions in the diluted magnetic semiconductor Zn$_{1}$$_{−}$$_{x}$Co$_{x}$O M. Kobayashi, 1, ∗ Y. Ishida, 1, † J. I. Hwang, 1 Y. Osafune, 1 A. Fujimori, 1 Y. Takeda, 2 T. Okane, 2 Y. Saitoh, 2 K. Kobayashi, 3 H. Saeki, 4 T. Kawai, 4 and H. Tabata 5, 6 $^{1}$Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan $^{2}$Synchrotron Radiation Research Unit, Japan Atomic Energy Agency, Sayo-gun, Hyogo 679-5148, Japan $^{3}$National Institute for Materials Science (NIMS), SPring-8, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan $^{4}$Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan $^{5}$Department of Electronic Engineering, School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan $^{6}$Department of Bioengineering, School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan (Dated: November 16, 2018) arXiv:1001.0712v1 [cond-mat.mtrl-sci] 5 Jan 2010 1