In Nuclear Magnetic Resonance (NMR), the gyromagnetic ratio ($\gamma$) is a fundamental property of a nucleus that determines how it behaves in a magnetic field.
The gyromagnetic ratio is defined as the ratio of the magnetic moment ($\mu$) to the angular momentum ($J$) of the nucleus:
\[
\gamma = \dfrac{\mu}{J}
\]
Since $J$ is typically fixed for a given nucleus, the gyromagnetic ratio $\gamma$ becomes directly proportional to the magnetic moment $\mu$.
This proportionality is essential in determining the resonance frequency of a nucleus in a magnetic field, which is given by:
\[
f = \dfrac{\gamma B}{2\pi}
\]
Thus, the correct relationship is: $\gamma \propto \mu$.