Low-field spin dynamics of Cr7Ni and Cr7Ni−Cu−Cr7Ni molecular rings as detected by μSR by Sanna, S, Arosio, P, Bordonali, L, Adelnia, F, Mariani, M, Garlatti, E, Baines, C, Amato, A, Sabareesh, KPV, Timco, G, Winpenny, REP, Blundell, SJ, Lascialfari, A