Exchange stiffness of ferromagnets M. D. Kuz’min, K. P. Skokov, L. V. B. Diop, I. A. Radulov and O. Gutfleisch Eur. Phys. J. Plus, 135 3 (2020) 301 Published online: 12 March 2020 DOI: 10.1140/epjp/s13360-020-00294-y