Evidence for a Jeff=0 ground state and defect-induced spin glass behavior in the pyrochlore osmate Y2Os2O7 ‌ Davies, N, Topping, C, Jacobsen, H, Princep, A, Kirschner, F, Rahn, M, Bristow, M, Vale, J, Da Silva, I, Baker, P, Sahle, C, Guo, Y, Yan, D, Shi, Y, Blundell, S, McMorrow, D, Boothroyd, A