  Nitrogen-vacancy quantum defects in diamond offer a promising platform for
magnetometry because of their remarkable optical and spin properties. In this
Letter, we present a high-sensitivity and wide-bandwidth fiber-based quantum
magnetometer for practical applications. By coating the diamond surface with
silver reflective film, both the fluorescence collection and excitation
efficiency are enhanced. Additionally, tracking pulsed optically detected
magnetic resonance spectrum allowed a magnetic field sensitivity of $35$
pT$/\sqrt{\rm{Hz}}$ and a bandwidth of $4.1$ KHz. Finally, this magnetometer
was successfully applied to map the magnetic field induced by the
current-carrying copper-wire mesh. Such a stable and compact magnetometry can
provide a powerful tool in many areas of physical, chemical, and biological
researches.
