EVIDENCE FOR EASY AXIS ROTATION IN DY1-XGDXAL2 ALLOYS FROM NUCLEAR HYPERFINE FIELD-MEASUREMENTS

We have studied the nuclear magnetic resonance of 163Dy in ferromagnetic Dy1-xGdxAl2 alloys (0?x?0.99). The observed behaviour of the resonance frequencies of the various resonances observed is anomalous and does not follow simple molecular field arguments. Quadrupolar splitting measurements suggest that within a given Dy environment of 0, 1, 2, 3 or 4 Gd nearest neighbours the Dy moment is independent of concentration of Gd. These results lead us to believe that the easy axis of magnetization rotates gradually from (100) to (111) in these compounds and that we in fact sense the Dy moment through nuclei in the domain wall edge. From enhancement factor measurements we conclude that the Dy single ion anisotropy is very small and that the predominate term, establishing domain wall stiffness, is the Dy-Dy interaction anisotropy.