Helical magnetism in Sr-doped CaMn7O12 films by Huon, A, Vibhakar, AM, Grutter, AJ, Borchers, JA, Disseler, S, Liu, Y, Tian, W, Orlandi, F, Manuel, P, Khalyavin, DD, Sharma, Y, Herklotz, A, Lee, HN, Fitzsimmons, MR, Johnson, RD, May, SJ