  We experimentally demonstrate that a squeezed probe optical field can improve
the sensitivity of the magnetic field measurements based on nonlinear
magneto-optical rotation (NMOR) with an amplitude-modulated pump when compared
to a coherent probe field under identical conditions. To realize an all-atomic
magnetometer prototype, we utilize a nonlinear atomic interaction, known as
polarization self-rotation(PSR), to produce a squeezed probe field. An
independent pump field, amplitude-modulated at the Larmor frequency of the bias
magnetic field, allows us to extend the range of most sensitive NMOR
measurements to sub-Gauss magnetic fields. While the overall sensitivity of the
magnetometer is rather low ($>250\mathrm{pT}/\sqrt{\mathrm{Hz}}$, we clearly
observe a $15\%$ sensitivity improvement when the squeezed probe is used. Our
observations confirm the recently reported quantum enhancement in a modulated
atomic magnetometer arXiv:2108.01519 [quant-ph].
