NMR in Domains and Walls in Ferromagnetic CrBr3

Nuclear magnetic resonance absorptions have been observed in zero applied field in the insulating ferromagnet CrBr3. Three lines are shown to be a quadrupole split triplet from nuclei in the bulk of the domains. A fourth, with a resonance frequency of 56.58 Mc at 1.34°K and a 250-kc linewidth, is ascribed to nuclei in the domain walls. The nuclear resonance frequencies are proportional to the local magnetization, and thus measure the temperature dependence of the magnetization both in domain walls and in domains. This is the first measurement of the difference between wall and domain magnetizations, and shows that (ΔM/M)wall − (ΔM/M)domain=T/200 in the spin wave region.