Audio-frequency spin absorption has been observed in the nuclear spin systems of the metals lithium, sodium, and aluminum. In lithium and sodium, the observed second moment of the absorption line at zero dc magnetic field is in agreement with calculations assuming only magnetic dipole-dipole interactions; in aluminum the zero-field absorption extends to frequencies as high as 50 kc/sec and the second moment of the absorption line appears to be about 50% larger than expected. Spin absorption has also been observed at small applied dc magnetic fields, $H_0$, for audio-frequency magnetic excitation both parallel to and perpendicular to $H_0$. In both of these cases, absorption occurs at $\gamma H_0$ and $2\gamma H_0$ in agreement with theory.

• Received 30 March 1959

DOI:https://doi.org/10.1103/PhysRev.115.863