DOMAIN-STRUCTURE DYNAMICS IN FERROMAGNETIC CRBR3 STUDIED BY NUCLEAR-MAGNETIC-RESONANCE

Nuclear magnetic resonance of Cr-53 in ferromagnetic CrBr3 in external magnetic fields was studied at 4.2 K. In zero field, a well-resolved NMR triplet (at 54.434 +/- 0.297 MHz) was observed from domains, a sin gle resonance (54.86 MHz) from domain walls, and a weak signal from Bl och lines (54.0 MHz). The NMR broadening, which is observed when the s aturation field is achieved (3.08 kOe for the field parallel to the c( 6)-axis), is explained by the inhomogeneous penetration of the field i nto the sheet-formed crystal. The signal intensities at different RF p olarizations indicate that the NMR enhancement coefficient is determin ed by the rotation of domain magnetization in the case of domains, and by the oscillatory motion of Bloch lines in the case of Bloch lines a nd domain walls. The ferromagnetic system does not shield the nuclei f rom the external magnetic field applied perpendicular to the c(6)-axis . Such a field removes the NMR degeneracy in domain walls, thus formin g a broad absorption band with distinct maxima. This band cannot be ex plained only in terms of the external field and the induced dipolar fi elds. The Cr+3 magnetization is assumed to depend, besides on orientat ion, on static gradients, which may be due to the spin-wave excitation and zero oscillations of domain walls and Bloch lines.