  We investigated, at temperature $4.2\,\mathrm{K}$, electric transport, flux
noise and resulting spin sensitivity of miniaturized Nb direct current
superconducting quantum interference devices (SQUIDs) based on submicron
Josephson junctions with HfTi barriers. The SQUIDs are either of the
magnetometer-type or gradiometric in layout. In the white noise regime, for the
best magnetometer we obtain a flux noise
$S_{\Phi}^{1/2}=250\,\mathrm{n}\Phi_0/\mathrm{Hz}^{1/2}$, corresponding to a
spin sensitivity $S^{1/2}_\mu\,\ge\,29\,\mu_B/\mathrm{Hz}^{1/2}$. For the
gradiometer we find $S_{\Phi}^{1/2}=300\,\mathrm{n}\Phi_0/\mathrm{Hz}^{1/2}$
and $S^{1/2}_\mu\,\ge\,44\,\mu_B/\mathrm{Hz}^{1/2}$. The devices can still be
optimized with respect to flux noise and coupling between a magnetic particle
and the SQUID, leaving room for further improvement towards single spin
resolution.
