NMR enhancement of a modulating field due to the anisotropic component of the hyperfine field in hcp Co and YCo5

Modulation of the ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ NMR spin-echo envelope in hcp Co and Y${\mathrm{Co}}_5$ results from the application of a small 80-kHz field. The modulating field is enhanced parallel to the local axis of quantization by an enhancement factor ${\eta }_{\parallel }$ which varies with position in the domain wall. The maximum enhancement factor is found to be ∼80 in hcp Co and ∼1000 in Y${\mathrm{Co}}_5$. When ${\eta }_{\parallel }$ is taken to arise from an anisotropic component of the hyperfine field it is estimated that this anisotropic component has a magnitude of 5.7 kOe in hexagonal Co and 60 kOe in Y${\mathrm{Co}}_5$.