Tuning optical and ferromagnetic properties of thin GdN films by nitrogen-vacancy centers Reddithota Vidyasagar, Shinya Kitayama, Hiroaki Yoshitomi, Takashi Kita, Takahiro Sakurai and Hitoshi Ohta Eur. Phys. J. B, 86 2 (2013) 52 Published online: 13 February 2013 DOI: 10.1140/epjb/e2012-30566-3