  We propose a novel type of magnetic scanning probe sensor, based on a single
planar Josephson junction with a magnetic barrier. The planar geometry together
with high magnetic permeability of the barrier helps to focus flux in the
junction and thus enhance the sensitivity of the sensor. As a result, it may
outperform equally sized SQUID both in terms of the magnetic field sensitivity
and the spatial resolution in one scanning direction. We fabricate and analyze
experimentally sensor prototypes with a superparamagnetic CuNi and a
ferromagnetic Ni barrier. We demonstrate that the planar geometry allows easy
miniaturization to nm-scale, facilitates an effective utilization of the
self-field phenomenon for amplification of sensitivity and a simple
implementation of a control line for feed-back operation in a broad dynamic
range.
