  We characterize the flux sensitivity of a dispersive 3D aluminum nanobridge
SQUID magnetometer as a function of applied in-plane magnetic field. In zero
field, we observe an effective flux noise of 17 n$\Phi_0$/Hz$^{1/2}$ with 25
MHz of bandwidth. Flux noise increased by less than a factor of three with
parallel magnetic fields up to 61 mT. Operation in higher fields may be
possible by decreasing the dimensions of the shunt capacitor in the
magnetometer circuit. These devices are thus well suited for observing
high-speed dynamics in nanoscale magnets, even in the presence of moderate bias
magnetic fields.
