A pulsed NMR study of narrow domain walls in DyAl₂

The results of a pulsed NMR study of the 27 Al resonance in DyAl 2 are presented and discussed. Quadrupole oscillations in the height of the spin-echo versus pulse separation tau have been found. The oscillations have been used to show that the magnetic hyperfine field at the 27 Al nuclei makes an angle of about 14.5 degrees with respect to the (001) direction of easy magnetisation. This result is consistent with an NMR signal originating either from within a domain or close to the edge of a narrow domain wall. In addition, a classical analysis of a 90 degrees domain wall in DyAl 2 is presented and used to compute RF enhancement factors eta , both within domain walls. It is shown, for example, that for an enhancement factor eta =500 at a Dy site the ratio of the crystal-field anisotropy to exchange (K/W) is about -0.035. This ratio is approximately six times smaller than a single crystal estimate of about -0.195, thereby implying that the 163 Dy NMR signal originates from domain walls, moving in regions of defects and imperfections.